Disambiguate get_ex_outlier_stream_rows query

A backwards-compatible piece of matrix-org#14979 that's safe to land now.

Author: David Robertson

synapse/storage/databases/main/events_worker.py

@@ -1779,7 +1779,7 @@ def get_ex_outlier_stream_rows_txn(
             txn: LoggingTransaction,
         ) -> List[Tuple[int, str, str, str, str, str, str, str, bool, bool]]:
             sql = (
-                "SELECT event_stream_ordering, e.event_id, e.room_id, e.type,"
+                "SELECT out.event_stream_ordering, e.event_id, e.room_id, e.type,"
                 " se.state_key, redacts, relates_to_id, membership, rejections.reason IS NOT NULL,"
                 " e.outlier"
                 " FROM events AS e"
@@ -1791,10 +1791,10 @@ def get_ex_outlier_stream_rows_txn(
                 " LEFT JOIN event_relations USING (event_id)"
                 " LEFT JOIN room_memberships USING (event_id)"
                 " LEFT JOIN rejections USING (event_id)"
-                " WHERE ? < event_stream_ordering"
-                " AND event_stream_ordering <= ?"
+                " WHERE ? < out.event_stream_ordering"
+                " AND out.event_stream_ordering <= ?"
                 " AND out.instance_name = ?"
-                " ORDER BY event_stream_ordering ASC"
+                " ORDER BY out.event_stream_ordering ASC"
             )
 
             txn.execute(sql, (last_id, current_id, instance_name))