* Remove pytest warnings
Ignore deprecations on Sphinx 9.0 that comes from readthedocs-sphinx-ext and use
`findall()` instead of `.traverse()` as suggested by docutils.
* We can't ignore a warning from Sphinx 9.0
We are testing in older versions where this exception is not defined.
The deprecation warning we are seeing here is not related to `sphinx_rtd_theme`
but with `readthedocs-sphinx-ext` because at:
13edf78bab/readthedocs_ext/readthedocs.py (L118-L122)
In any case, we will stop using that Sphinx extension at some point.
* Tests: Fix deprecation warning with new sphinx versions
These builders where split in sphinx and the old import path will be removed in the upcoming Sphinx 4 release.
This patch requires sphinx 2 so this will be committed into the v2 release.
* Fix imports
* Use try/except for backwards compatibility
