$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-u-tae2-9177-27989/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-tae2-9177-27989/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 7243cfcc969d306f03aee0a15ef3dcfba93a02e8:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         7243cfcc969d306f03aee0a15ef3dcfba93a02e8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7243cfc bump release for test build