Add additional Python 3.9 CI tests

[rwedge]

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[codecov]

Codecov Report

Merging #1934 (6de0ab4) into main (f058111) will not change coverage.
The diff coverage is n/a.

❗ Current head 6de0ab4 differs from pull request most recent head 1d2d432. Consider uploading reports for the commit 1d2d432 to get more accurate results

@@           Coverage Diff           @@
##             main    #1934   +/-   ##
=======================================
  Coverage   98.99%   98.99%           
=======================================
  Files         146      146           
  Lines       16438    16438           
=======================================
  Hits        16273    16273           
  Misses        165      165           

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