$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-u-ysionneau1-9434-28179/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-ysionneau1-9434-28179/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 667815c10c05a1db0ab7d5ef1c3e4143feb32133:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         667815c10c05a1db0ab7d5ef1c3e4143feb32133 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 667815c bump release for test build