$ git clone -n https://src.fedoraproject.org/rpms/rubygem-syck.git /var/lib/mock/f40-build-733987-105636/root/chroot_tmpdir/scmroot/rubygem-syck
Cloning into '/var/lib/mock/f40-build-733987-105636/root/chroot_tmpdir/scmroot/rubygem-syck'...
$ git fetch origin 819d10c6b2b5ccc69b26ec13d70adc008c6a0dad:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-syck
 * [new ref]         819d10c6b2b5ccc69b26ec13d70adc008c6a0dad -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 819d10c Backport upstream patch for Regexp.new 3rd argument removal