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.

👻

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.38%. Comparing base (d776d14) to head (94c6500).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #220      +/-   ##
==========================================
+ Coverage   95.37%   95.38%   +0.01%     
==========================================
  Files          37       37              
  Lines        3245     3253       +8     
==========================================
+ Hits         3095     3103       +8     
  Misses        150      150              

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[braingram]

Thanks!