Update Read the Docs build OS

[AndreyVMarkelov]

Summary

Update the Read the Docs build image from ubuntu-20.04 to ubuntu-24.04.

Why

Read the Docs no longer accepts ubuntu-20.04, causing build 33520151 to fail during config validation before dependencies or Sphinx run.

Impact

Documentation builds can proceed on a supported LTS image.

Validation

• YAML parses successfully.
• git diff --check passes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.19%. Comparing base (e0008c8) to head (f96a175).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #539   +/-   ##
=======================================
  Coverage   65.19%   65.19%           
=======================================
  Files          32       32           
  Lines       55001    55001           
  Branches     3911     3911           
=======================================
  Hits        35858    35858           
  Misses      18988    18988           
  Partials      155      155           

Flag	Coverage Δ
integration	65.01% <ø> (ø)
unit	64.75% <ø> (ø)

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