$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-u-tae1-10212-28783/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-tae1-10212-28783/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin aedfc44c56c4055e4c0ec491dd9b819212ec8a40:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         aedfc44c56c4055e4c0ec491dd9b819212ec8a40 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at aedfc44 bump release for test build