Python 3.8 was removed from the tested runtimes for 2024.2[1] and has
not been tested since then.
Also add Python 3.12 which is part of the tested runtimes for 2025.1.
Now unit tests job with Python 3.12 is voting.
[1] https://governance.openstack.org/tc/reference/runtimes/2024.2.html
Change-Id: I657fa65af42e41ca2f57b726cc70a7fc2569e3d9
Switch to openstackdocstheme 2.2.1 and reno 3.1.0 versions. Using
these versions will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems
Update Sphinx version as well.
Disable openstackdocs_auto_version to not auto-version the documents.
Disable openstackdocs_auto_name to use 'project' variable as name.
Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.
Remove docs requirements from lower-constraints, they are not needed
during install or test but only for docs building.
openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.
See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html
Change-Id: I26cabdc85596be44fca36cad2a609b8fca0e50e0