x11/xdg-desktop-portal-luminous: update to 0.1.8

Changes: https://github.com/waycrate/xdg-desktop-portal-luminous/releases/tag/v0.1.7
Changes: https://github.com/waycrate/xdg-desktop-portal-luminous/releases/tag/v0.1.8
Reported by: GitHub (watch releases)

(cherry picked from commit 651086be4fd415514865828f47fde072c7e1953a)