$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-incoming-10206-28716/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-10206-28716/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin b4bc53c441642cbc5c76455ce819246728f5dcb1:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         b4bc53c441642cbc5c76455ce819246728f5dcb1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b4bc53c Add support for Intel CPU sensors (through xenpm)