fix: sorting on "Modified By" in chart table (#16208)

* initial fix

* Update ChartList.tsx

change sort to first name

superset-frontend/src/views/CRUD/chart/ChartList.tsx

@@ -285,7 +285,7 @@ function ChartList(props: ChartListProps) {
           </a>
         ),
         Header: t('Modified by'),
-        accessor: 'last_saved_by',
+        accessor: 'last_saved_by.first_name',
         size: 'xl',
       },
       {