chore: stub gtk_native_dialog_get_type (#34141)

shell/browser/ui/electron_gtk.sigs

@@ -3,4 +3,5 @@ void gtk_native_dialog_set_modal(GtkNativeDialog* self, gboolean modal);
 void gtk_native_dialog_show(GtkNativeDialog* self);
 void gtk_native_dialog_hide(GtkNativeDialog* self);
 gint gtk_native_dialog_run(GtkNativeDialog* self);
-void gtk_native_dialog_destroy(GtkNativeDialog* self);
+void gtk_native_dialog_destroy(GtkNativeDialog* self);
+GType gtk_native_dialog_get_type(void);