Correct type hint for room_batch.py (#11310)

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

changelog.d/11310.misc

@@ -0,0 +1 @@
+Add type hints to storage classes.

mypy.ini

@@ -46,7 +46,6 @@ exclude = (?x)
    |synapse/storage/databases/main/push_rule.py
    |synapse/storage/databases/main/receipts.py
    |synapse/storage/databases/main/room.py
-   |synapse/storage/databases/main/room_batch.py
    |synapse/storage/databases/main/roommember.py
    |synapse/storage/databases/main/search.py
    |synapse/storage/databases/main/signatures.py
@@ -183,6 +182,9 @@ disallow_untyped_defs = True
 [mypy-synapse.storage.databases.main.client_ips]
 disallow_untyped_defs = True
 
+[mypy-synapse.storage.databases.main.room_batch]
+disallow_untyped_defs = True
+
 [mypy-synapse.storage.util.*]
 disallow_untyped_defs = True
 

synapse/storage/databases/main/room_batch.py

@@ -39,13 +39,11 @@ class RoomBatchStore(SQLBaseStore):
 
     async def store_state_group_id_for_event_id(
         self, event_id: str, state_group_id: int
-    ) -> Optional[str]:
-        {
-            await self.db_pool.simple_upsert(
-                table="event_to_state_groups",
-                keyvalues={"event_id": event_id},
-                values={"state_group": state_group_id, "event_id": event_id},
-                # Unique constraint on event_id so we don't have to lock
-                lock=False,
-            )
-        }
+    ) -> None:
+        await self.db_pool.simple_upsert(
+            table="event_to_state_groups",
+            keyvalues={"event_id": event_id},
+            values={"state_group": state_group_id, "event_id": event_id},
+            # Unique constraint on event_id so we don't have to lock
+            lock=False,
+        )