match Field TypeVar variance in models.fields.related

[asottile]

previously failing with:

_____________________________ foreign_key_subclass _____________________________
/home/asottile/workspace/django-stubs/tests/typecheck/fields/test_related.yml:90: 
E   pytest_mypy_plugins.utils.TypecheckAssertionError: Invalid output: 
E   Actual:
E     myapp/models:7: error: Variance of TypeVar "_ST" incompatible with variance in parent type  [type-var] (diff)
E     myapp/models:7: error: Variance of TypeVar "_GT" incompatible with variance in parent type  [type-var] (diff)
E   Expected:
E     (empty)

I'm not sure how this wasn't a problem before 5.0.4 for us but it certainly is now!

I'm also surprised mypy doesn't report this same error for related.pyi itself -- there must be some special-cased rules that .pyi files don't have to follow

[asottile]

failure looks like a github flake

[sobolevn]

Thank you!

Source:

django-stubs/django-stubs/db/models/fields/__init__.pyi

Lines 47 to 52 in 04eed10

	# __set__ value type
	_ST = TypeVar("_ST", contravariant=True)
	# __get__ return type
	_GT = TypeVar("_GT", covariant=True)
	class Field(RegisterLookupMixin, Generic[_ST, _GT]):