Remove EOL versions of Python & Django

[jsma]

Removes Python 3.6 which was EOL as of 2021-12-23, and Django 2.2 which was EOL as of 2022-04-11 Updates Github actions to latest versions

[codecov[bot]]

Codecov Report

Merging #225 (829d945) into master (97441f1) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #225   +/-   ##
=======================================
  Coverage   93.88%   93.88%           
=======================================
  Files          10       10           
  Lines         523      523           
  Branches       66       66           
=======================================
  Hits          491      491           
  Misses         19       19           
  Partials       13       13           

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