Sphinx 7.3 made some changes that broke some configuration meddling that

we do in the autodocs extension. This change adds compatibility and

tests for all 7.x releases.
It also fixes some test regressions largely caused by newer releases of

the Sphinx ecosystem that broke prior versions of Sphinx. We lock down

dependencies in our tox.ini for many of these builds. This will hold

us over until we drop older versions of Sphinx in newer releases.

All unit tests in all tox environments pass.