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/misc/util.js

@@ -182,7 +182,7 @@ export function trySpawnCommandLine(commandLine) {
 }
 
 function _handleSpawnError(command, err) {
-    let title = _("Execution of “%s” failed:").format(command);
+    let title = _('Execution of “%s” failed:').format(command);
     Main.notifyError(title, err.message);
 }