$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-10278-28844/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-10278-28844/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 4d50634e08aa4af94c056dbe012d381703cbf666:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         4d50634e08aa4af94c056dbe012d381703cbf666 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4d50634 Merge pull request #81 from xcp-ng-rpms/8.3-import_xen-4.17.6-2.xs8.src.rpm