Support typing.Unpack in Sphinx builds

[redeboer]

If the signature of a function contains typing.Unpack, Sphinx autodoc crashes if it is run on Python 3.10 or lower. The reason is that autodoc needs Unpack.__name__, which exists if importing from typing, but not if importing from typing_extensions.

The solution is to run the documentation workflow, RTD, and the Conda environment in Python 3.11 or higher. This would have to be added as an option in the check-dev-files hook. See e.g. this log from ComPWA/ampform#365.