$ git clone -n https://github.com/xcp-ng-rpms/xen.git /var/lib/mock/v8.3-incoming-10256-28831/root/chroot_tmpdir/scmroot/xen
Cloning into '/var/lib/mock/v8.3-incoming-10256-28831/root/chroot_tmpdir/scmroot/xen'...
$ git fetch origin 046a878923c4a536d01be6adcc6d9d1d0e2d2460:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/xen
 * [new ref]         046a878923c4a536d01be6adcc6d9d1d0e2d2460 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 046a878 Merge branch 'XS-8.3' into 8.3-import_xen-4.17.6-2.xs8.src.rpm