pybind11

Fix data race when using shared variables (free threading) (#5494)

* Fix data race when using shared variables (free threading)

In the free threading build, there's a race between wrapper re-use and
wrapper deallocation. This can happen with a static variable accessed by
multiple threads.

Fixing this requires using some private CPython APIs: _Py_TryIncref and
_PyObject_SetMaybeWeakref. The implementations of these functions are
included until they're made available as public ("unstable") APIs.

Fixes #5489

* style: pre-commit fixes

* Avoid unused parameter

* Add missing return for default build

* Changes from review

* Assign result to local variable

* s/clang-tidy/ruff

* clang-tidy: static is redundant

* Use 'noqa: B018'

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Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>