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this had three sets of breakage addressed by other PRs:

- our foreign key subclass was not functioning, django-stubs added a
default TypeVar here which started getting filled in with an unbound
TypeVar resulting in thousands of errors: fixed by
#75228
- we were able to remove our fork's [descriptor
patch](getsentry/sentry-forked-django-stubs#4)
(which removed the non-model overload of `__get__` for fields) as mypy
[fixed this issue](python/mypy#17381). in doing
so it pointed out an unsafe descriptor access through a mixin and so
that had to go: #75360
- django-stubs improved some field validation through QuerySets which
was only checked through managers before: fixed by
#75359