Fix a bad merge from release-v1.20.0. (#8354)

changelog.d/8354.misc

+Fix bad merge from `release-v1.20.0` branch to `develop`.

synapse/handlers/pagination.py

@@ -385,7 +385,7 @@ class PaginationHandler:
                         )
 
                 await self.hs.get_handlers().federation_handler.maybe_backfill(
-                    room_id, curr_topo, limit=source_config.limit,
+                    room_id, curr_topo, limit=pagin_config.limit,
                 )
 
             to_room_key = None