py-pybind11: updated to 2.9.0

Version 2.9.0
This is the last version to support Python 2.7 and 3.5.

New Features:

Allow py::args to be followed by other arguments; the remaining arguments are implicitly keyword-only, as if a py::kw_only{} annotation had been used.

Changes:

Make str/bytes/memoryview more interoperable with std::string_view.
Replace _ with const_name in internals, avoid defining pybind::_ if _ defined as macro (common gettext usage)

Bug fixes:

Fix a rare warning about extra copy in an Eigen constructor.
Fix caching of the C++ overrides.
Add missing std::forward calls to some cpp_function overloads.
Support PyPy 7.3.7 and the PyPy3.8 beta. Test python-3.11 on PRs with the python dev label.
Replace usage of deprecated Eigen::MappedSparseMatrix with Eigen::Map<Eigen::SparseMatrix<...>> for Eigen 3.3+.
Tweaks to support Microsoft Visual Studio 2022.

Build system improvements:

Nicer CMake printout and IDE organisation for pybind11's own tests.
CMake: report version type as part of the version string to avoid a spurious space in the package status message.
Flags starting with -g in $CFLAGS and $CPPFLAGS are no longer overridden by .Pybind11Extension.
Ensure ThreadPool is closed in setup_helpers.
Avoid LTS on mips64 and ppc64le (reported broken).

(adam)