$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-fasttrack-9322-28078/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-fasttrack-9322-28078/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 811dc87b6c2dbf126606e64f6df191e16a5d3d9f:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         811dc87b6c2dbf126606e64f6df191e16a5d3d9f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 811dc87 Merge pull request #71 from xcp-ng-rpms/8.3-xsa472