cleanup: Always use single quotes

We have made good progress with transitioning to the new style,
to the point where we can complete it with a final push.

Start with changing the remaining places that still use double
quotes.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2866>

js/ui/appDisplay.js

@@ -1770,7 +1770,7 @@ class AppDisplay extends BaseAppView {
         let appItems = apps.map(id => this._items.get(id).app);
         let folderName = _findBestFolderName(appItems);
         if (!folderName)
-            folderName = _("Unnamed Folder");
+            folderName = _('Unnamed Folder');
 
         newFolderSettings.delay();
         newFolderSettings.set_string('name', folderName);