$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-9671-28393/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-9671-28393/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 9e86fd5f6d2185547418e5d2d198b6fa21be00e4:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         9e86fd5f6d2185547418e5d2d198b6fa21be00e4 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 9e86fd5 Merge pull request #75 from xcp-ng-rpms/8.3-import_xen-4.17.5-21.xs8.src.rpm