Add gis_admin_deprecations fixer

[fitoria]

Allows replacement of OSMGeoAdmin and GeoModelAdmin with GISModelAdmin from the same module, those classe were removed on Django 5.0: https://docs.djangoproject.com/en/5.0/releases/5.0/#django-contrib-gis

[adamchainz]

Oh great. I haven't got time for a full review right now, but at a glance it’s looking good. Can you add a changelog note?

Little note for the future - please don't make PRs from the main branch of your fork, but create a branch. It makes it easier for maintainers to push edits back and be sure that things don't break.

[fitoria]

Ready!

[adamchainz]

This would be a Django 4.0 fixer, because that's when the classes were deprecated. I have moved it there.

I looked at the code as of Django 4.0. It looks like we can't blindly rewrite model admin classes to use GISModelAdmin in the case that they define any of the 29 attributes provided by the old classes: https://github.com/django/django/blob/4555aa0a489cb9dcf764edf12339097cdfa5ff84/django/contrib/gis/admin/options.py#L43-L71 . Doing so could break functionality.

Those attributes could also come from multiple inheritance, which should also mean that a safe automated fix is impossible.

So I think we should add two restrictions:

1. Only rewrite model admin classes that inherit from exactly one class, with no keyword arguments (i.e. not class F(OSMGeoAdmin, something=1):, just in case)
2. Ignore any classes that have any the 29 attributes defined in their class bodies.

Do you think you could update to add these, and appropriate tests?

[fitoria]

Do you think you could update to add these, and appropriate tests?

Sure, I'm going to take care of it, thanks for the review.

[adamchainz]

Hey, I am just gearing up for a release here, so I took a look at your PR. It needs quite a bit of work to limit the fixer to class definitions and add the above restrictions. I pushed two new, failing tests that represent the restrictions, and will leave the PR like this for now. Let me know if you find time to work on this again (no pressure!).