Remove django-celery-beat/setuptools workaround

[nijel]

Describe the issue

eb19b33 needs to be reverted once celery/django-celery-beat#772 is fixed (and fix released).

Additional context

• [BUG] Many packages are no longer installable after test command is removed pypa/setuptools#4519
• [FR] More gradual breakage of setuptools.command.test pypa/setuptools#4520
• ModuleNotFoundError: No module named 'setuptools.command.test' astral-sh/uv#5551

[github-actions]

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