$ git clone -n https://src.fedoraproject.org/rpms/rubygem-cairo.git /var/lib/mock/f42-build-865331-173025/root/chroot_tmpdir/scmroot/rubygem-cairo
Cloning into '/var/lib/mock/f42-build-865331-173025/root/chroot_tmpdir/scmroot/rubygem-cairo'...
$ git fetch origin b053fc987d728c45a35ff2dc75a7a6a5bee8d647:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-cairo
 * [new ref]         b053fc987d728c45a35ff2dc75a7a6a5bee8d647 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b053fc9 1.17.4