$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-fasttrack-11342-29657/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-fasttrack-11342-29657/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 3453b2a59f3984ad171c76c8d937246bba2339dc:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         3453b2a59f3984ad171c76c8d937246bba2339dc -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3453b2a Merge pull request #84 from xcp-ng-rpms/dnt/4.17.6-5.2