Increasing default piano staff spacing

[Jin Choi]

I have a passage of piano music with a lot of kneed beams between the staves, 
and there’s too few objects above the bass staff to force enough space. How can 
I increase the default spacing between the treble and bass parts of the piano 
staff?

Here’s an example. The “dim.” clashes with the beam on beat 1, and beat 4 in 
the bass is just a mess.

\version "2.24.1"

top = { \change Staff = "upper" \voiceTwo }
bottom = { \change Staff = "lower" \voiceOne }

upper = \relative c'' {
  \key g \minor
  \new Voice {
    \voiceOne
    g8\(\dim gis\! a4\)~ a8\(^\markup {\italic "poco rit."} bes \tuplet 3/2 { c 
d ees\) } |  
  }
}

lower = \relative {
  \clef bass
  \key g \minor
  \new Voice {
      \voiceOne
      bes16 b \top d f
      \bottom b, c \top ees f 
      \bottom g, c \top  ees f
      \bottom a, g' \top ees \bottom f |  
  }
}


\score {
  \new PianoStaff {
    <<
    \new Staff = "upper" \upper
    \new Staff = "lower" \lower
    >>
  }
}