$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v9.0-u-ydi1-11541-29857/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v9.0-u-ydi1-11541-29857/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 0210181e8664f0b7481cabe0d74a1c6959d6adc7:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         0210181e8664f0b7481cabe0d74a1c6959d6adc7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0210181 bump release for test build