Provide fake depth to builder of temp event for auth calculation

This prevents an unnecessary query to fetch the depth of the event which
we never need to store.

Author: Fizzadar

synapse/handlers/message.py

@@ -1045,7 +1045,9 @@ async def create_new_client_event(
             temp_event = await builder.build(
                 prev_event_ids=prev_event_ids,
                 auth_event_ids=state_event_ids,
-                depth=depth,
+                # Always provide depth here to avoid unncessary lookup from the events
+                # table; we've no need for the depth of this temp event to be correct.
+                depth=0,
             )
             state_events = await self.store.get_events_as_list(state_event_ids)
             # Create a StateMap[str]