user parameter for login accepts None (#496)

Co-authored-by: Gilad Sheffer <[email protected]>

Author: giladsheffer

django-stubs/contrib/auth/__init__.pyi

@@ -23,7 +23,7 @@ def load_backend(path: str) -> ModelBackend: ...
 def get_backends() -> List[ModelBackend]: ...
 def authenticate(request: Any = ..., **credentials: Any) -> Optional[AbstractBaseUser]: ...
 def login(
-    request: HttpRequest, user: AbstractBaseUser, backend: Optional[Union[Type[ModelBackend], str]] = ...
+    request: HttpRequest, user: Optional[AbstractBaseUser], backend: Optional[Union[Type[ModelBackend], str]] = ...
 ) -> None: ...
 def logout(request: HttpRequest) -> None: ...
 def get_user_model() -> Type[Model]: ...