ci: Add testing against django main

[marksweb]

This adds testing against django's main branch.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ecac82f) 90.88% compared to head (9bcb377) 90.88%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #353   +/-   ##
=======================================
  Coverage   90.88%   90.88%           
=======================================
  Files          72       72           
  Lines        2546     2546           
  Branches      361      361           
=======================================
  Hits         2314     2314           
  Misses        168      168           
  Partials       64       64           

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[fsbraun]

@marksweb You'll need to also swap installation of requirements and django main branch.

[fsbraun]

@marksweb Should we test the Django main branch with django CMS develop-4 ?

[fsbraun]

@marksweb Does it make sense to run the py3.12 against develop-4 for the time being?

[marksweb]

@fsbraun not if support might take a while.

[fsbraun]

I think it's there.

[fsbraun]

@marksweb I added the following lines to the three test files that use assertQuerySetEqual just after the imports:

if not hasattr(CMSTestCase, "assertQuerySetEqual"):
    # Django < 4.2
    CMSTestCase.assertQuerySetEqual = CMSTestCase.assertQuerysetEqual

Might be easier to remove later...