xfce4-settings: update to 4.18.4

4.18.4 (2023-11-30)
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- display-settings: Fix memory management of confirmation dialog
- xfsettingsd: displays: Always do some actions on RRScreenChangeNotify
- xfsettingsd: displays: Fix memory leak
- settings-manager: Support absolute path as icon name
- Replace deprecated xfce_spawn(_command_line)?_on_screen
- appearance: Match more dark themes (fixes #495)
- appearance: Check for presence of color-scheme key
- Apply matching xfwm4 when the switch is clicked
- displays: Lower warning level
- Translation Updates:
  Basque, Czech, Danish, French, Greek, Kazakh, Lithuanian, Occitan
  (post 1500)

(gutteridge)