Fixed typo in MiddlewareMixin deprecation note.

docs/internals/deprecation.txt

@@ -114,7 +114,7 @@ details on these changes.
 * Support for the pre-Django 3.1 user sessions (that use the SHA-1 algorithm)
   will be removed.
 
-* The ``get_request`` argument for
+* The ``get_response`` argument for
   ``django.utils.deprecation.MiddlewareMixin.__init__()`` will be required and
   won't accept ``None``.
 

docs/releases/4.0.txt

@@ -524,7 +524,7 @@ to remove usage of these features.
 * Support for the pre-Django 3.1 user sessions (that use the SHA-1 algorithm)
   is removed.
 
-* The ``get_request`` argument for
+* The ``get_response`` argument for
   ``django.utils.deprecation.MiddlewareMixin.__init__()`` is required and
   doesn't accept ``None``.