[WIP] Enable Read the Docs check on pull requests

[Codex]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>pipeline: readthedocs is now enabled, and should appear as a check on PRs</issue_title>
<issue_description></issue_description>

<agent_instructions>examine the readthedocs build/config from fre-cli https://github.com/NOAA-GFDL/fre-cli/blob/main/.readthedocs.yaml</agent_instructions>

Comments on the Issue (you are @codex[agent] in this section)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main      #55   +/-   ##
=======================================
  Coverage        ?   61.63%           
=======================================
  Files           ?        9           
  Lines           ?     1199           
  Branches        ?        0           
=======================================
  Hits            ?      739           
  Misses          ?      460           
  Partials        ?        0           

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