$ git clone -n https://github.com/xcp-ng-rpms/expat.git /var/lib/mock/v8.3-incoming-9125-27948/root/chroot_tmpdir/scmroot/expat
Cloning into '/var/lib/mock/v8.3-incoming-9125-27948/root/chroot_tmpdir/scmroot/expat'...
$ git fetch origin a841a9b34dd02b625ba5c4a0712974b29322abc8:KOJI_FETCH_HEAD
From https://github.com/xcp-ng-rpms/expat
 * [new ref]         a841a9b34dd02b625ba5c4a0712974b29322abc8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a841a9b Import expat-2.5.0-3.xs8.src.rpm