Fix get_users_in_room mis-use in transfer_room_state_on_room_upgrade (#13960)

Spawning from looking into `get_users_in_room` while investigating #13942 (comment).

See #13575 (comment) for the original exploration around finding `get_users_in_room` mis-uses.

Related to the following PRs where we also cleaned up some `get_users_in_room` mis-uses:

 - #13605
 - #13608
 - #13606
 - #13958

Author: MadLittleMods

changelog.d/13960.misc

@@ -0,0 +1 @@
+Use dedicated `get_local_users_in_room(room_id)` function to find local users when calculating users to copy over during a room upgrade.

synapse/handlers/room_member.py

@@ -1150,8 +1150,8 @@ async def transfer_room_state_on_room_upgrade(
         logger.info("Transferring room state from %s to %s", old_room_id, room_id)
 
         # Find all local users that were in the old room and copy over each user's state
-        users = await self.store.get_users_in_room(old_room_id)
-        await self.copy_user_state_on_room_upgrade(old_room_id, room_id, users)
+        local_users = await self.store.get_local_users_in_room(old_room_id)
+        await self.copy_user_state_on_room_upgrade(old_room_id, room_id, local_users)
 
         # Add new room to the room directory if the old room was there
         # Remove old room from the room directory