tox: Add sphinx environments to check sane doc build
Enable to check package documentation can be built without producing sphinx warnings.
The sphinx
environment is designed to be used in continuous integration
in order to prevent breaking documentation build when committing changes.
The sphinx-dev
environment is designed to be used inside a full swh
development environment.
Related to T3258
Also add a commit to fix a sphinx warning since rDDOCa8ca608e4f532c203bfae126ebbe324cc82392b0.
Migrated from D5593 (view on Phabricator)