$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-u-prebuild-9264-28049/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-prebuild-9264-28049/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 40ba46319f3eb44db0824856ab3fecfa8684aace:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         40ba46319f3eb44db0824856ab3fecfa8684aace -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 40ba463 bump release for test build