$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-u-prebuild-9263-28049/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-u-prebuild-9263-28049/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 49938b14434b61ebfe9d6e5ff3dba4d077c0bec2:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         49938b14434b61ebfe9d6e5ff3dba4d077c0bec2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 49938b1 bump release for test build