$ git clone -n https://src.fedoraproject.org/rpms/papers.git /var/lib/mock/f45-build-43753-805/root/chroot_tmpdir/scmroot/papers
Cloning into '/var/lib/mock/f45-build-43753-805/root/chroot_tmpdir/scmroot/papers'...
$ git fetch origin dd2f6456ea5c6a047e655c3f23bce237d42864c1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/papers
 * [new ref]         dd2f6456ea5c6a047e655c3f23bce237d42864c1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at dd2f645 Update to 51.0