chore(deps): update greenlet requirement from <3.5.0 to <3.6.0 in /backend

[dependabot]

Updates the requirements on greenlet to permit the latest version.

Changelog

Sourced from greenlet's changelog.

3.5.0 (2026-04-27)

• Remove the atexit callback. This callback caused greenlet APIs to become unavailable far too soon during interpreter shutdown. Now they remain available while all atexit callbacks run. Sometime after Py_IsFinalizing becomes true, they may begin misbehaving. Because the order in which C extensions are finalized is undefined, C extensions that are sensitive to this need to check the results of that function before invoking greenlet APIs. As a convenience, PyGreenlet_GetCurrent sets an exception and returns NULL when this happens (and greenlet.getcurrent begins returning None); other greenlet C API functions have undefined behaviour. Methods invoked directly on pre-existing greenlet.greenlet objects will continue to function at least until the greenlet C extension has been garbage collected and finalized.

  See PR 508 <https://github.com/python-greenlet/greenlet/pull/508>_.

3.4.0 (2026-04-08)

• Publish binary wheels for RiscV 64.

• Fix multiple rare crash paths during interpreter shutdown.

  Note that this now relies on the atexit module, and introduces subtle API changes during interpreter shutdown (for example, getcurrent is no longer available once the atexit callback fires).

  See PR [#499](https://github.com/python-greenlet/greenlet/issues/499) <https://github.com/python-greenlet/greenlet/pull/499>_ by Nicolas Bouvrette.

• Address the results of an automated code audit performed by Daniel Diniz. This includes several minor correctness changes that theoretically could have been crashing bugs, but typically only in very rare circumstances.

  See PR 502 <https://github.com/python-greenlet/greenlet/pull/502>_.

• Fix several race conditions that could arise in free-threaded builds when using greenlet objects from multiple threads, some of which could lead to assertion failures or interpreter crashes.

  See issue 503 <https://github.com/python-greenlet/greenlet/issues/503>_, with thanks to Nitay Dariel and Daniel Diniz.

3.3.2 (2026-02-20)

... (truncated)

Commits

• c7acc72 Preparing release 3.5.0
• d08f99b CHANGES: Update link from #507 to more full description in #508.
• fd3391e Merge pull request #508 from python-greenlet/issue507-remove-atexit
• 004e1e9 Remove the atexit callback.
• b784a69 Back to development: 3.4.1
• df6734e Preparing release 3.4.0
• 0f86075 Merge pull request #504 from python-greenlet/freethreading-fixes
• 4596574 TLBC: crash appears to still happen on CI 3.14t ubuntu. Re-enable workaround.
• 2f4a1cf Make green_switch (python level greenlet.switch) and green_throw check for (p...
• a0c2a2a Fix unused variable warning when asserts are disabled.
• Additional commits viewable in compare view

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