Mixing harmonics and regular notes

In passages where there are harmonics in one voice and regular notes in the other, the note head 'style override only applies to the voice in which it is declared.

\version "2.24"

%% http://lsr.di.unimi.it/LSR/Item?id=539

upper = \relative c' {
  \voiceOne
  \clef "treble_8"
  \override NoteHead.style = #'harmonic
  g8 a b c b4 d
  <g b>1
}

lower = \relative c {
  \voiceTwo
  \clef "treble_8"
  e2 d
  g,1
}

\score {
  \new Staff = "guitar" <<
    \context Voice = "upper" { \upper }
    \context Voice = "lower" { \lower }
  >>
  \layout { }
}