Fix tombstone handling

Author: tulir

github/bot.py

@@ -67,6 +67,7 @@ async def start(self) -> None:
         self.register_handler_class(self.webhook_receiver)
         self.register_handler_class(self.clients)
         self.register_handler_class(self.commands)
+        self.register_handler_class(self.webhook_manager)
 
     async def reset_tokens(self) -> None:
         try:

github/db.py

@@ -218,7 +218,7 @@ async def transfer_webhook_repo(self, id: uuid.UUID, new_repo: str) -> None:
 
     async def transfer_webhook_rooms(self, old_room: RoomID, new_room: RoomID) -> None:
         await self.db.execute(
-            "UPDATE webhook SET room_id = $1 WHERE room_id = $2 ON CONFLICT (repo, room_id) DO NOTHING",
+            "UPDATE webhook SET room_id = $1 WHERE room_id = $2",
             new_room,
             old_room,
         )