Fix invalidating OTK count cache after claim (#10875)

The invalidation was missing in `_claim_e2e_one_time_key_returning`,
which is used on SQLite 3.24+ and Postgres. This could break e2ee if
nothing else happened to invalidate the caches before the keys ran out.

Signed-off-by: Tulir Asokan <[email protected]>

Author: tulir

changelog.d/10875.bugfix

@@ -0,0 +1 @@
+Fix invalidating one-time key count cache after claiming keys. Contributed by Tulir at Beeper.

synapse/storage/databases/main/end_to_end_keys.py

@@ -824,6 +824,10 @@ def _claim_e2e_one_time_key_returning(
             if otk_row is None:
                 return None
 
+            self._invalidate_cache_and_stream(
+                txn, self.count_e2e_one_time_keys, (user_id, device_id)
+            )
+
             key_id, key_json = otk_row
             return f"{algorithm}:{key_id}", key_json