Increase number of old rooms to delete nightly

scripts/matrix/clean-old-rooms.sh

@@ -4,7 +4,7 @@ set -eou pipefail
 # Get the list of rooms with no local users
 empty_rooms() {
     psql -d synapse -c "SELECT room_id FROM room_stats_current WHERE local_users_in_room = 0 \
-        ORDER BY current_state_events DESC LIMIT 1;" -t --csv
+        ORDER BY current_state_events DESC LIMIT 3;" -t --csv
 }
 
 # Delete a room and purge its history