chore: update reference os and python for read-the-docs

[karel-rehor]

Proposed Changes

Update base python and ubuntu image. Troubleshooting why read-the-docs has suddenly started failing.

Checklist

• [ ] CHANGELOG.md updated N.A. CI only
• Rebased/mergeable
• [] A test has been added if appropriate N.A.
• [] Tests pass
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.38%. Comparing base (7e83f32) to head (b3a9db1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #248      +/-   ##
==========================================
+ Coverage   86.34%   86.38%   +0.04%     
==========================================
  Files          28       28              
  Lines        2072     2072              
==========================================
+ Hits         1789     1790       +1     
+ Misses        283      282       -1     

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[NguyenHoangSon96]

LGTM 🚀