Test number of queries executed in room create test

Author: Fizzadar

tests/rest/client/test_rooms.py

@@ -708,6 +708,8 @@ def test_post_room_no_keys(self) -> None:
 
         self.assertEqual(200, channel.code, channel.result)
         self.assertTrue("room_id" in channel.json_body)
+        assert channel.resource_usage is not None
+        self.assertEqual(33, channel.resource_usage.db_txn_count)
 
     def test_post_room_visibility_key(self) -> None:
         # POST with visibility config key, expect new room id