fix formatstring

exporter.py

@@ -22,7 +22,7 @@ def fetch_metrics(synapse_url, access_token):
     update_room_metrics(rooms)
 
     for room in rooms:
-        statefile = f'state/{room['room_id']}.end'
+        statefile = f"state/{room['room_id']}.end"
         url = f"{synapse_url}/_synapse/admin/v1/rooms/{room['room_id']}/messages"
         messages = []