Enable systemd for GNOME ui packages

@craftyguy thinks we should enable systemd for gnome/gnome-mobile by default. plamo and phosh also do this. Users who want to use openrc can still disable it with pmbootstrap config systemd never

cc @pabloyoyoista @Newbyte

old summary

(this patch was originally sent to fix some unrelated issue below)

When building with pmabootstrap config systemd default, pmboostrap install fails with:

(rootfs_oneplus-enchilada) % setup-timezone -i Europe/Berlin
/bin/sh: setup-timezone: not found

Tested locally and this fixes the build step.

main/postmarketos-ui-gnome/APKBUILD

@@ -26,7 +26,7 @@ _pmb_recommends="
 	"
 subpackages="$pkgname-openrc"
 source="firefox-wayland.sh"
-options="!check"
+options="!check pmb:systemd"
 
 package() {
 	install -Dm755 \