$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v9.0-u-ydi1-11137-29553/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v9.0-u-ydi1-11137-29553/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin ef5b782ffc985eaff5bd6080a1439cbd36e1d1c6:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         ef5b782ffc985eaff5bd6080a1439cbd36e1d1c6 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ef5b782 bump release for test build