Fix override_config test decorator on Django 5.2

[pfouque]

Yet another Django 5.2 fix:

Django 5.2 is the first version to ship this PR turning pre_setup into a classmethod and generating this error (already visible in tox, but ignored)

  ERROR: test_override_config_on_class_changes_config_value (tests.test_test_overrides.OverrideConfigClassDecoratorTestCase.test_override_config_on_class_changes_config_value)
  Assert that the class decorator changes config.BOOL_VALUE.
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/home/runner/work/django-constance/django-constance/constance/test/unittest.py", line 49, in _pre_setup
      original_pre_setup(inner_self)
  TypeError: TransactionTestCase._pre_setup() takes 1 positional argument but 2 were given

I found this fix, following the current solution but maybe a better (and more modern) solution exists
"""
Override the config by modifying TestCase methods.

This method follows the Django <= 1.6 method of overriding the
_pre_setup and _post_teardown hooks rather than modifying the TestCase
itself.
"""

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.82%. Comparing base (1451943) to head (1ea167f).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #609      +/-   ##
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+ Coverage   84.23%   84.82%   +0.58%     
==========================================
  Files          21       21              
  Lines         736      751      +15     
  Branches      117      122       +5     
==========================================
+ Hits          620      637      +17     
+ Misses         83       82       -1     
+ Partials       33       32       -1     

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[pfouque]

FYI: I added Django 5.2 to the test matrix (to catch other potential issues).
it's pointing to the alpha release so it will have to be updated

[Natim]

Can we create a decorator for that so that we don't have to duplicate the code of the method?

[pfouque]

The decorator is not the only difference, the call to original_pre_setup also differs (as we don't have to pass the instance anymore)
Additionally, this version is probably easier to clean up when Django5.2 will be the minimum supported version