DOCS: Updated readthedocs dependency

[tkknight]

🚀 Pull Request

Description

Updated readthedocs dependency

RTD Docs on this: https://docs.readthedocs.com/platform/stable/config-file/v2.html#build-tools-python

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[scitools-ci]

Templating

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Template candidates

The following changed files are not currently templated, but their parent directories suggest they may be good candidates for a new template to be created:

• .readthedocs.yml

Footnotes

1. Include this text in the PR body to avoid any notifications about applying the template changes back to the source repo!
   @scitools-templating: please no update notification on: iris ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.12%. Comparing base (781376b) to head (9e0d69d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7084   +/-   ##
=======================================
  Coverage   90.12%   90.12%           
=======================================
  Files          91       91           
  Lines       24951    24951           
  Branches     4683     4683           
=======================================
  Hits        22488    22488           
  Misses       1684     1684           
  Partials      779      779           

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