$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v9.0-u-ydi1-11139-29553/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v9.0-u-ydi1-11139-29553/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin c3cad07b208cb1c6d6baebbbbfb03dcfb4ba0a2c:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         c3cad07b208cb1c6d6baebbbbfb03dcfb4ba0a2c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c3cad07 bump release for test build