$ git clone -n https://github.com/xcp-ng-rpms/xen /var/lib/mock/v8.3-u-tae1-10211-28783/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-tae1-10211-28783/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin c4b2c6f90b944e59bbe869f2f9f78800a270300f:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         c4b2c6f90b944e59bbe869f2f9f78800a270300f -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c4b2c6f bump release for test build