$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-11151-29564/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-11151-29564/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 0f740cf5cbde49c88d5dd9eb919a6a1db2a35343:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         0f740cf5cbde49c88d5dd9eb919a6a1db2a35343 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0f740cf Merge pull request #83 from xcp-ng-rpms/8.3-import_xen-4.17.6-5.xs8.src.rpm