$ git clone -n https://src.fedoraproject.org/rpms/rpm-ostree.git /var/lib/mock/f40-build-792580-138446/root/chroot_tmpdir/scmroot/rpm-ostree
Cloning into '/var/lib/mock/f40-build-792580-138446/root/chroot_tmpdir/scmroot/rpm-ostree'...
$ git fetch origin 7573c80fef7e32966c046fafd93bfff771854d28:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rpm-ostree
 * [new ref]         7573c80fef7e32966c046fafd93bfff771854d28 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7573c80 Backport: https://github.com/coreos/rpm-ostree/commit/fe586621e5014d14f92b913338171a02ed29e6cc