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.

3.5.1 (2026-05-20)

• Add preliminary support for Python 3.15b1. This has not been reviewed by CPython core developers, but all tests pass. Binary wheels of this version won't work on earlier Python 3.15 builds and may not work on later 3.15 builds.
• Fix the discrepancy in the way the two getcurrent APIs behave during greenlet teardown. One API (the C API used by, e.g., gevent) raised a RuntimeError; the other (the Python greenlet.getcurrent API) returned None. This second way is incompatible with greenlet's type annotations, so greenlet.getcurrent now raises a RuntimeError as well.

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

... (truncated)

Commits

• b5e5fc4 Preparing release 3.5.1
• c8e1774 Tweak wording in CHANGES about greenlet.getcurrent.
• 7fb10c5 Merge pull request #510 from python-greenlet/315
• 9718ce5 Add Py 3.15; make both API versions of getcurrent() consistent in raising Run...
• 276e08a Merge pull request #509 from python-greenlet/dependabot/github_actions/github...
• 32b0ad6 Bump pypa/gh-action-pypi-publish in the github-actions group
• 173b692 Back to development: 3.5.1
• 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
• Additional commits viewable in compare view

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