$ git clone -n https://src.fedoraproject.org/rpms/rubygem-glib2.git /var/lib/mock/f40-build-733948-105594/root/chroot_tmpdir/scmroot/rubygem-glib2
Cloning into '/var/lib/mock/f40-build-733948-105594/root/chroot_tmpdir/scmroot/rubygem-glib2'...
$ git fetch origin fc4632d9090b1ca147d8cf0c0418162e4272e472:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-glib2
 * [new ref]         fc4632d9090b1ca147d8cf0c0418162e4272e472 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at fc4632d 4.2.0 entry