Add pyo3::sync::with_critical_section2 binding

[XuehaiPan]

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Add pyo3::sync::with_critical_section2 binding for Py_{BEGIN,END}_CRITICAL_SECTION2 macros.

For free-threading builds, some functions need to be run with two objects locked. E.g. PyDict_Update(dict, other), dequeiter_next(it, it->deque).

[davidhewitt]

Thanks, overall looks good to me, however I would like to see a different test.