Fix Admin on Django 5.2

[pfouque]

Early testing the upgrade to Django 5.2, I'm facing an issue with Django-constance admin:

  File "/home/runner/work/silvr-app/silvr-app/silvr-app/.venv/lib/python3.12/site-packages/constance/admin.py", line 194, in <module>
    admin.site.register([Config], ConstanceAdmin)
  File "/home/runner/work/silvr-app/silvr-app/silvr-app/.venv/lib/python3.12/site-packages/django/contrib/admin/sites.py", line 116, in register
    if model._meta.is_composite_pk:
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Meta' object has no attribute 'is_composite_pk'

Indeed, Django last/next version provides composite primary keys which requires a new Meta on Models.
Due to the fake Config model django Constance is using, we need to do likes for other properties and hardcode it on the Config.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.69%. Comparing base (1451943) to head (062ccf7).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #608      +/-   ##
==========================================
+ Coverage   84.23%   84.69%   +0.45%     
==========================================
  Files          21       21              
  Lines         736      745       +9     
  Branches      117      121       +4     
==========================================
+ Hits          620      631      +11     
+ Misses         83       82       -1     
+ Partials       33       32       -1     

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[pfouque]

Thanks @Natim and @Mogost !

[Mogost]

Released in 4.3.1