Update Rust crate pyo3 to 0.21.2

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
pyo3	dependencies	patch	0.21 -> 0.21.2

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Release Notes

pyo3/pyo3 (pyo3)

v0.21.2

Compare Source

Changed

• Deprecate the PySet::empty() gil-ref constructor. #​4082

Fixed

• Fix compile error for async fn in #[pymethods] with a &self receiver and more than one additional argument. #​4035
• Improve error message for wrong receiver type in __traverse__. #​4045
• Fix compile error when exporting a #[pyclass] living in a different Rust module using the experimental-declarative-modules feature. #​4054
• Fix missing_docs lint triggering on documented #[pymodule] functions. #​4067
• Fix undefined symbol errors for extension modules on AIX (by linking libpython). #​4073

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