Adjust some version pins and roundup roundup

[nutjob4life]

🗒️ Summary

• Adjust some version pins both in setup metadata and in the processing of Python packages (Sphinx 3.2.1)
• Explicitly use the Roundup's own (i.e., the container's) Python and not the virtual environment's Python
  • The virtual environment's Python is for the package being "rounded up"
  • The container's Python is for Roundup Action itself
• 👉 Note: These changes won't work unless pds-github-util has a new @stable tag merged from this PR as well

⚙️ Test Data and/or Report

See: https://github.com/nasa-pds-engineering-node/sumo-tools/actions/runs/4056685843

♻️ Related Issues

• 105

[jordanpadams]

@nutjob4life to confirm, whenever we tag a new version of pds-github-util and push to pypi, we should also be tagging a new stable release to support roundup?

[nutjob4life]

@jordanpadams absolutely! Same applies to roundup-action.

(Note that roundup-action's Dockerfile installs pds-github-util directly from GitHub, not PyPI, so the push to PyPI step is just gravy.)

I'll take care of tagging stable for both.