Add bug number

Author: schmidt-sebastian

packages/firestore/src/core/sync_engine_impl.ts

@@ -619,7 +619,7 @@ export async function syncEngineRejectListen(
     let documentUpdates = new SortedMap<DocumentKey, MutableDocument>(
       DocumentKey.comparator
     );
-    // TODO(mrschmidt): This limbo document should ideally have a read time,
+    // TODO(b/217189216): This limbo document should ideally have a read time,
     // so that it is picked up by any read-time based scans. The backend,
     // however, does not send a read time for target removals.
     documentUpdates = documentUpdates.insert(