quick-settings: Add ellipses to 'Log Out' string

According to GNOME HIG, if an item opens a new window or dialog,
it should be indicated with ellipses.

This change adds ellipses to the "Log Out" menu item
in the quick access menu.

Fixes #5821

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2467>

js/ui/status/system.js

@@ -183,7 +183,7 @@ class ShutdownItem extends QuickSettingsItem {
 
         this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
 
-        this._addSystemAction(_('Log Out'), 'can-logout', () => {
+        this._addSystemAction(_('Log Out…'), 'can-logout', () => {
             this._systemActions.activateLogout();
             Main.panel.closeQuickSettings();
         });