Fix webhook remove

[OliveiraHermogenes]

The arguments to get_by_repo were being passed in the wrong order.

github/github/webhook/manager.py

Lines 76 to 78 in 3d19ccc

	async def get_by_repo(self, room_id: RoomID, repo: str) -> WebhookInfo | None:
	return self._add_to_cache(await self._db.get_webhook_by_repo(room_id, repo))

[OliveiraHermogenes]

A screenshot of the behavior before the fix:

[tulir]

Not sure how that wasn't noticed before 🤔