$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v9.0-u-ydi1-11375-29683/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v9.0-u-ydi1-11375-29683/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 821de43a97048c75be9479d9b4077f6da05eb04e:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         821de43a97048c75be9479d9b4077f6da05eb04e -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 821de43 bump release for test build