$ git clone -n https://src.fedoraproject.org/rpms/rubygem-glib2.git /var/lib/mock/f45-build-34941-692/root/chroot_tmpdir/scmroot/rubygem-glib2
Cloning into '/var/lib/mock/f45-build-34941-692/root/chroot_tmpdir/scmroot/rubygem-glib2'...
$ git fetch origin c29aded159df0a89aa4451faff8842245ecf9b87:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-glib2
 * [new ref]         c29aded159df0a89aa4451faff8842245ecf9b87 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c29aded update file entry