flakey test on macos /w python 3.9

[grahamgower]

Maybe a reentrancy issue? There seem to be multiple failure modes. Here is one:

tests/test_plot.py::TestPlotHist::test_plot_hist[-] 
Current thread 0x0000700002f1a000 (most recent call first):
[gw1] node down: Not properly terminated
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/backends/backend_macosx.py", line 150 in __init__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 2858 in create_with_canvas
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 1742 in new_manager
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 3579 in new_figure_manager_given_figure
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/backend_bases.py", line 3574 in new_figure_manager
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/pyplot.py", line 384 in new_figure_manager
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/pyplot.py", line 840 in figure
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/_api/deprecation.py", line 454 in wrapper
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/matplotlib/pyplot.py", line 1501 in subplots
  File "/Users/runner/work/dinf/dinf/dinf/plot.py", line 683 in __call__
  File "/Users/runner/work/dinf/dinf/dinf/plot.py", line 1214 in main
  File "/Users/runner/work/dinf/dinf/tests/test_plot.py", line 61 in test_plot_demes
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/python.py", line 195 in pytest_pyfunc_call
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_callers.py", line 39 in _multicall
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_manager.py", line 80 in _hookexec
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_hooks.py", line 265 in __call__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/python.py", line 1789 in runtest
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 167 in pytest_runtest_call
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_callers.py", line 39 in _multicall
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_manager.py", line 80 in _hookexec
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_hooks.py", line 265 in __call__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 260 in <lambda>
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 339 in from_call
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 259 in call_runtest_hook
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 220 in call_and_report
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 131 in runtestprotocol
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/runner.py", line 112 in pytest_runtest_protocol
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_callers.py", line 39 in _multicall
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_manager.py", line 80 in _hookexec
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_hooks.py", line 265 in __call__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/xdist/remote.py", line 174 in run_one_test
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/xdist/remote.py", line 157 in pytest_runtestloop
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_callers.py", line 39 in _multicall
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_manager.py", line 80 in _hookexec
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_hooks.py", line 265 in __call__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/main.py", line 324 in _main
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/main.py", line 270 in wrap_session
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/_pytest/main.py", line 317 in pytest_cmdline_main
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_callers.py", line 39 in _multicall
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_manager.py", line 80 in _hookexec
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/pluggy/_hooks.py", line 265 in __call__
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/xdist/remote.py", line 355 in <module>
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 1084 in executetask
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 220 in run
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 285 in _perform_spawn

Thread 0x0000700001f17000 (most recent call first):
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 400 in read
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 432 in from_io
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 967 in _thread_receiver
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 220 in run
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 285 in _perform_spawn

Thread 0x0000000111143dc0 (most recent call first):
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/threading.py", line 312 in wait
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/threading.py", line 581 in wait
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 263 in integrate_as_primary_thread
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 1060 in serve
  File "/Users/runner/hostedtoolcache/Python/3.9.14/x64/lib/python3.9/site-packages/execnet/gateway_base.py", line 1554 in serve
  File "<string>", line 8 in <module>
  File "<string>", line 1 in <module>
[gw1] [ 72%] FAILED tests/test_plot.py::TestPlotDemes::test_plot_demes