arch_boxes_sync: Pull the artifacts from GitLab's package registry

arch-boxes has decided to use GitLab's package registry instead of job artifacts[1].

[1] arch-boxes@d04c8274

roles/arch_boxes_sync/files/arch-boxes-sync.service

@@ -6,4 +6,4 @@ Type=oneshot
 ExecStart=/usr/local/bin/arch-boxes-sync.sh
 ProtectSystem=strict
 PrivateTmp=true
-ReadWritePaths=/srv/ftp/images
+ReadWritePaths=/srv/ftp/lastupdate /srv/ftp/images