$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v9.0-u-ydi1-11096-29521/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v9.0-u-ydi1-11096-29521/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin b7c744c23e2da69fc5eac35a635874ac174beb1a:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         b7c744c23e2da69fc5eac35a635874ac174beb1a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b7c744c bump release for test build