[4.1.x] Fixed #34062 -- Updated View.http_method_not_allowed() to support async.

As with the options() methods, wrap the response in a coroutine if
the view is async.

Co-authored-by: Carlton Gibson <carlton.gibson@noumenal.es>

Backport of 9b0c9821ed from main

django/views/generic/base.py

@@ -148,7 +148,16 @@ class View:
             request.path,
             extra={"status_code": 405, "request": request},
         )
-        return HttpResponseNotAllowed(self._allowed_methods())
+        response = HttpResponseNotAllowed(self._allowed_methods())
+
+        if self.view_is_async:
+
+            async def func():
+                return response
+
+            return func()
+        else:
+            return response
 
     def options(self, request, *args, **kwargs):
         """Handle responding to requests for the OPTIONS HTTP verb."""