Tests

Improve reachability in narrowing logic #20420

Job	Run time
Test mypyc suite with 32-bit Python	9m 29s
Type check our own code (py310-windows-64)	2m 27s
Test suite with py310-ubuntu, mypyc-compiled	14m 16s
mypyc runtime tests with py310-ubuntu	5m 42s
mypyc runtime tests with py313-macos	5m 39s
Test suite with py314t-ubuntu, mypyc-compiled	15m 17s
Test suite with py314-windows-64	15m 14s
Test suite with py312-ubuntu	8m 43s
Test suite with py311-ubuntu	8m 54s
Parallel tests with py314-ubuntu, interpreted	15m 20s
Test suite with py314-ubuntu, mypyc-compiled	14m 11s
Test suite with py313-ubuntu, mypyc-compiled	14m 4s
Parallel tests with py314-ubuntu, mypyc-compiled	15m 19s
Type check our own code (py310-ubuntu)	1m 41s
Formatting and code style with Black + ruff	1m 50s
	2h 28m 6s

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