theme: Include both dark and light variant in resource

This will allow us to switch between the variants according to
the color-scheme setting.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5545

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2324>

js/ui/sessionMode.js

@@ -22,7 +22,7 @@ if (Config.HAVE_NETWORKMANAGER)
 const _modes = {
     'restrictive': {
         parentMode: null,
-        stylesheetName: 'gnome-shell.css',
+        stylesheetName: 'gnome-shell-dark.css',
         themeResourceName: 'gnome-shell-theme.gresource',
         hasOverview: false,
         showCalendarEvents: false,