Add Django 4.0 support

[Dresdn]

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Checklist

• I have double checked that there are no unrelated changes in this pull request (old patches, accidental config files, etc.)
• I have created at least one test case for the changes I have made
• I have updated the documentation for the changes I have made
• I have added my changes to the CHANGELOG.md

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

Related issue(s)

Closes #136

Other Information

[codecov]

Codecov Report

Merging #138 (5b267c2) into master (ed7a808) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #138      +/-   ##
==========================================
+ Coverage   87.44%   87.50%   +0.05%     
==========================================
  Files          20       20              
  Lines         741      744       +3     
  Branches      134      134              
==========================================
+ Hits          648      651       +3     
  Misses         71       71              
  Partials       22       22              

Impacted Files	Coverage Δ
eav/models.py	97.20% <0.00%> (+0.03%)	⬆️

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