Stop depending on room_id to be returned for children state in the hierarchy response.

changelog.d/12991.bugfix

@@ -0,0 +1,2 @@
+Fix a bug where non-standard information was required when requesting the `/hierarchy` API over federation. Introduced 
+in Synapse v1.41.0.

synapse/federation/federation_client.py

@@ -1642,10 +1642,6 @@ def _validate_hierarchy_event(d: JsonDict) -> None:
     if not isinstance(event_type, str):
         raise ValueError("Invalid event: 'event_type' must be a str")
 
-    room_id = d.get("room_id")
-    if not isinstance(room_id, str):
-        raise ValueError("Invalid event: 'room_id' must be a str")
-
     state_key = d.get("state_key")
     if not isinstance(state_key, str):
         raise ValueError("Invalid event: 'state_key' must be a str")

tests/handlers/test_room_summary.py

@@ -178,7 +178,7 @@ def _assert_hierarchy(
             result_room_ids.append(result_room["room_id"])
             result_children_ids.append(
                 [
-                    (cs["room_id"], cs["state_key"])
+                    (result_room["room_id"], cs["state_key"])
                     for cs in result_room["children_state"]
                 ]
             )