For APKBUILD linting we care only about APKBUILD files that were changed,
not to which package they belong or whatever.
The "with_directory" option of get_changed_packages() really meant
"just give me changed files", which means that we can just use
get_changed_files() instead.
Since we copy these aports directly from Alpine and try to keep them in
sync, we don't want to differ from upstream because our CI doesn't pass
on linting. If the APKBUILD should be improved, it should be done
upstream which is then synced back to us.
