Add Django 4.1 support

[kevinmarsh]

Only a small change was required in the tests to handle this change about removing the type="text/css" attributes for CSS link tags:

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It might make sense when releasing a new version to drop support for Python 3.6 and Django 2.2, 3.0 and 3.1 since they have all reached end of life. If you want I can push that in this PR or seperately

[codecov]

Codecov Report

Merging #774 (0c2821f) into master (c85a257) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #774   +/-   ##
=======================================
  Coverage   80.75%   80.75%           
=======================================
  Files          33       33           
  Lines        1143     1143           
=======================================
  Hits          923      923           
  Misses        220      220           

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[exallium]

From the looks of it, the changeset here only appears to cover test files and workflows, correct? The current version of django-pipelines should still be ok to utilize in a 4.1 project? (Genuine question. I still think this PR is important regardless of the answer!)

[kevinmarsh]

Yea we've been using the latest (2.0.8) django-pipeline release with Django 4.1 (on Python 3.10) in production for a couple months and it's been fine (for the narrow case we're using it for). So this PR was just updating the testing matrix and classifiers so the package "officially" supports Django 4.1

[kevinmarsh]

Looks like this got released in #786