$ git clone -n https://src.fedoraproject.org/rpms/rubygem-nokogiri.git /var/lib/mock/f42-build-side-1-3510481-46033/root/chroot_tmpdir/scmroot/rubygem-nokogiri
Cloning into '/var/lib/mock/f42-build-side-1-3510481-46033/root/chroot_tmpdir/scmroot/rubygem-nokogiri'...
$ git fetch origin 31378a8aa8b07d4f8cfc956af4dfe8d5dbe9ccb0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-nokogiri
 * [new ref]         31378a8aa8b07d4f8cfc956af4dfe8d5dbe9ccb0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 31378a8 1.18.8