do_delete_user: Make the replacement dummy user inactive.

Otherwise, the dummy user will show up in the user list in the right
sidebar.

zerver/lib/actions.py

@@ -1228,6 +1228,7 @@ def do_delete_user(user_profile: UserProfile) -> None:
         password=None,
         realm=realm,
         full_name=f"Deleted User {user_id}",
+        active=False,
         is_mirror_dummy=True,
     )
     subs_to_recreate = [

zerver/tests/test_users.py

@@ -2071,6 +2071,7 @@ class DeleteUserTest(ZulipTestCase):
             replacement_dummy_user.delivery_email, f"deleteduser{hamlet_user_id}@{realm.uri}"
         )
         self.assertEqual(replacement_dummy_user.is_mirror_dummy, True)
+        self.assertEqual(replacement_dummy_user.is_active, False)
 
         self.assertEqual(Message.objects.filter(id__in=personal_message_ids_to_hamlet).count(), 0)
         # Huddle messages from hamlet should have been deleted, but messages of other participants should