Fix release 0.38.0

Replace `@@plpythonu@@` vars in old_versions

server/extension/old_versions/cdb_dataservices_server--0.30.2--0.30.3.sql

@@ -67,4 +67,4 @@ RETURNS SETOF cdb_dataservices_server.isoline AS $$
     raise Exception('Error trying to get Mapbox isolines')
   finally:
     service_manager.quota_service.increment_total_service_use()
-$$ LANGUAGE plpythonu SECURITY DEFINER STABLE PARALLEL RESTRICTED;
+$$ LANGUAGE @@plpythonu@@ SECURITY DEFINER STABLE PARALLEL RESTRICTED;