build: Manually pull some RTD Context.

[feanil]

See https://about.readthedocs.com/blog/2024/07/addons-by-default/ for details but
essentially RTD is changing how it's building docs and this will let us handle the
change gracefully.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.12%. Comparing base (a33db7f) to head (0258970).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2236   +/-   ##
=======================================
  Coverage   95.12%   95.12%           
=======================================
  Files         195      195           
  Lines       21601    21601           
  Branches     1936     1936           
=======================================
  Hits        20547    20547           
  Misses        786      786           
  Partials      268      268           

Flag	Coverage Δ
unittests	95.12% <ø> (ø)

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