temp/gnome-shell-mobile: drop gnome-themes-standard dependency
Depend on gnome-themes-extra instead of gnome-themes-standard. Follows
the same change from Alpine's regular gnome-shell package.
Fix for upstream-compat check:
missing depend(s): gnome-themes-standard
Related: https://gitlab.alpinelinux.org/alpine/aports/-/commit/959ad322e0cb616257443206fd3ca85f7492012d