$ git clone -n https://src.fedoraproject.org/rpms/mkvtoolnix.git /var/lib/mock/f39-build-1793050-41752/root/chroot_tmpdir/scmroot/mkvtoolnix
Cloning into '/var/lib/mock/f39-build-1793050-41752/root/chroot_tmpdir/scmroot/mkvtoolnix'...
$ git fetch origin 2cf57187235615d078e98f0020b217b2eeed92ff:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/mkvtoolnix
 * [new ref]         2cf57187235615d078e98f0020b217b2eeed92ff -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2cf5718 Merge branch 'f38' into f39