Fix doc build and workflow job name.

[jezdez]

I've noticed that the documentation build was broken after looking into the 2.0.0 release and found it to be related to sphinx-doc/sphinx#9811, one of the many incarnations of docutils 0.18 containing breaking changes for Sphinx. This pins to docutils<0.18 to work around it for now.

I've also took the liberty to enable pull request building for the docs via Read The Docs, so we see build issues earlier, see the pull request jobs/checks below. The preview is here: https://django-taggit--768.org.readthedocs.build/en/768/

[codecov]

Codecov Report

Merging #768 (ae5017a) into master (cfca412) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #768   +/-   ##
=======================================
  Coverage   90.30%   90.30%           
=======================================
  Files           9        9           
  Lines         712      712           
  Branches      111      111           
=======================================
  Hits          643      643           
  Misses         45       45           
  Partials       24       24           

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[jezdez]

Thanks @auvipy!