Fix MiddlewareMixin.__call__() return type (#1595)

* fix: #1594 MiddlewareMixin.__call__ -- Return type incompatible with supertype

Co-authored-by: Marti Raudsepp <marti@juffo.org>

Author: GabDug

django-stubs/utils/deprecation.pyi

@@ -42,5 +42,5 @@ class MiddlewareMixin:
 
     get_response: _GetResponseCallable | _AsyncGetResponseCallable
     def __init__(self, get_response: _GetResponseCallable | _AsyncGetResponseCallable) -> None: ...
-    def __call__(self, request: HttpRequest) -> HttpResponseBase: ...
+    def __call__(self, request: HttpRequest) -> HttpResponseBase | Awaitable[HttpResponseBase]: ...
     async def __acall__(self, request: HttpRequest) -> HttpResponseBase: ...

tests/typecheck/utils/test_deprecation.yml

@@ -0,0 +1,13 @@
+-   case: basic_middleware_mixin_test
+    main: |
+      from typing import Union
+
+      from django.utils.deprecation import MiddlewareMixin
+      from django.http import HttpRequest, HttpResponseBase
+      from collections.abc import Awaitable
+
+      class MyMiddleware(MiddlewareMixin):
+          def __call__(
+              self, request: HttpRequest
+          ) -> Union[HttpResponseBase, Awaitable[HttpResponseBase]]:
+              return self.get_response(request)