$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-u-stormi1-8823-27766/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-stormi1-8823-27766/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 971e99ae0a5dd2639e1d70487693efe2efea666a:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         971e99ae0a5dd2639e1d70487693efe2efea666a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 971e99a bump release for test build