git-ignore the correct build output dir for the old UI

Signed-off-by: Julius Volz <julius.volz@gmail.com>

.gitignore

@@ -22,7 +22,7 @@ benchmark.txt
 /documentation/examples/remote_storage/example_write_adapter/example_write_adapter
 
 npm_licenses.tar.bz2
-/web/ui/static/react-app
+/web/ui/static/react
 /web/ui/static/mantine-ui
 
 /vendor