$ git clone -n https://src.fedoraproject.org/rpms/mkvtoolnix.git /var/lib/mock/f40-build-1507877-23891/root/chroot_tmpdir/scmroot/mkvtoolnix
Cloning into '/var/lib/mock/f40-build-1507877-23891/root/chroot_tmpdir/scmroot/mkvtoolnix'...
$ git fetch origin 6a756ad9482418a22a8feef430ba1625b47e6e79:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mkvtoolnix
 * [new ref]         6a756ad9482418a22a8feef430ba1625b47e6e79 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6a756ad Merge branch 'f39' into f40