extensionPrefs: Use new Extensions proxy

We will soon sandbox the application, so it makes sense to not request
more access than strictly necessary (even with priviledged access like
extension management).

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1106

js/extensionPrefs/js/main.js

@@ -64,7 +64,9 @@ class Application extends Gtk.Application {
             provider,
             Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION);
 
-        this._shellProxy = new GnomeShellProxy(Gio.DBus.session, 'org.gnome.Shell', '/org/gnome/Shell');
+        this._shellProxy = new GnomeShellProxy(Gio.DBus.session,
+            'org.gnome.Shell.Extensions', '/org/gnome/Shell/Extensions');
+
         this._window = new ExtensionsWindow({ application: this });
     }
 });