Pin sphinx themes more strictly

[QuLogic]

PR Summary

As discussed on the call today.

PR Checklist

Documentation and Tests

• [n/a] Has pytest style unit tests (and pytest passes)
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• [n/a] New plotting related features are documented with examples.

Release Notes

• [n/a] New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• [n/a] API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• [n/a] Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst

[QuLogic]

Actually, I know this is going to conflict with v3.7.x due to #25307, so I'll just do the backport myself manually after merging, and not bother meeseeksdev with it.

[jklymak]

Would be nice to add to environment.yml as well...