Update .readthedocs.yml configuration

[marshallward]

Newest Read the Docs configuration file requires explicit specification of the environment (using build:). This patch includes this section.

Upgrading to newer Python environments has also forced us to specify an older Jinja2 that works with our legacy Sphinx module.

[marshallward]

This is a very minor PR which only modifies Read The Docs configuration. Currently, our documentation generation does not work and gives an error.

Although documentation is produced from the NOAA-GFDL fork, it is generated from our copy of main, so we need this to go through the MOM-ocean fork before we can update our own copy.

This should not affect the others in any way and should be quick to approve.

[codecov]

Codecov Report

Merging #1613 (9ea8074) into main (f6b6b0b) will not change coverage.
The diff coverage is n/a.

❗ Current head 9ea8074 differs from pull request most recent head e41929e. Consider uploading reports for the commit e41929e to get more accurate results

@@           Coverage Diff           @@
##             main    #1613   +/-   ##
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  Coverage   37.91%   37.91%           
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  Files         269      269           
  Lines       77155    77155           
  Branches    14164    14164           
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  Hits        29254    29254           
  Misses      42623    42623           
  Partials     5278     5278           

see 1 file with indirect coverage changes

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[marshallward]

Reminder to have a look at this PR. It is only to fix a minor documentation issue.