Properly invalidate get_thread_id cache. (#14163)

This was missed in 2b6d41e (#13824).

Author: clokep

changelog.d/14163.feature

@@ -0,0 +1 @@
+Support for thread-specific notifications & receipts ([MSC3771](https://github.com/matrix-org/matrix-spec-proposals/pull/3771) and [MSC3773](https://github.com/matrix-org/matrix-spec-proposals/pull/3773)).

synapse/storage/databases/main/cache.py

@@ -244,6 +244,7 @@ def _invalidate_caches_for_event(
             # redacted.
             self._attempt_to_invalidate_cache("get_relations_for_event", (redacts,))
             self._attempt_to_invalidate_cache("get_applicable_edit", (redacts,))
+            self._attempt_to_invalidate_cache("get_thread_id", (redacts,))
 
         if etype == EventTypes.Member:
             self._membership_stream_cache.entity_has_changed(state_key, stream_ordering)