Fix rotating existing notifications in push summary (#14138)

Broke by #14045. Fixes #14120.

Introduced in v1.69.0rc2.

changelog.d/14138.bugfix

@@ -0,0 +1 @@
+Fix error in background update when rotating existing notifications. Introduced in v1.69.0rc2.

synapse/storage/databases/main/event_push_actions.py

@@ -1104,11 +1104,13 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
             )
 
             # First ensure that the existing rows have an updated thread_id field.
-            self.db_pool.simple_update_txn(
-                txn,
-                table="event_push_summary",
-                keyvalues={"room_id": room_id, "user_id": user_id, "thread_id": None},
-                updatevalues={"thread_id": "main"},
+            txn.execute(
+                """
+                UPDATE event_push_summary
+                SET thread_id = ?
+                WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+                """,
+                ("main", room_id, user_id),
             )
 
             # Replace the previous summary with the new counts.
@@ -1272,6 +1274,14 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
         logger.info("Rotating notifications, handling %d rows", len(summaries))
 
         # Ensure that any updated threads have an updated thread_id.
+        txn.execute_batch(
+            """
+            UPDATE event_push_summary
+            SET thread_id = ?
+            WHERE room_id = ? AND user_id = ? AND thread_id is NULL
+            """,
+            [("main", room_id, user_id) for user_id, room_id in summaries],
+        )
         self.db_pool.simple_update_many_txn(
             txn,
             table="event_push_summary",