fix: handle null `py::handle` and add tests for `py::scoped_critical_section`#5706

henryiii merged 19 commits intopybind:masterpybind/pybind11:masterfrom

XuehaiPan:handle-null-for-scoped_critical_sectionXuehaiPan/pybind11:handle-null-for-scoped_critical_sectionCopy head branch name to clipboard