MNT: Replace ubuntu-20.04 with ubuntu-22.04

[pllim]

As recommended by actions/runner-images#11101 , this PR replaces the deprecated ubuntu-20.04 runner with a newer version. This also replaces RTD workflow, if applicable, to future-proof the build in case it follows suit.

This is an automated update made by the batchpr tool 🤖 - feel free to close if it doesn't look good! You can report issues to @pllim.

👻

[github-actions]

Thank you for your contribution! 🌌 This checklist is meant to remind the package maintainers who will review this pull request of some common things to look for.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the STScI coding guidelines?
• Are tests added/updated as required? If so, do they follow the STScI testing guidelines?
• Are docs added/updated as required?
• Is rebase and/or squash necessary? If so, please provide the author with appropriate instructions.
• Did the CI pass? If no, are the failures related?
• Is a change log needed?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.19%. Comparing base (262a309) to head (022b181).
Report is 22 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #405   +/-   ##
=======================================
  Coverage   97.19%   97.19%           
=======================================
  Files          17       17           
  Lines        2031     2031           
=======================================
  Hits         1974     1974           
  Misses         57       57           

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