shell/util: Use gtk4 for week-start fallback
If langinfo isn't available, we determine the week start via a "magic" string translation from GTK. We currently look up the string in GTK3's domain, we should use GTK4's instead.
If langinfo isn't available, we determine the week start via a "magic" string translation from GTK. We currently look up the string in GTK3's domain, we should use GTK4's instead.