Double bar line as system start

A double bar line as system start may be printed as demonstrated here.

\version "2.24"

\layout {
  \context {
  	\Score
  	\override SystemStartBar.thickness = 1.8
  }
  \context {
    \StaffGroup
    \override Clef.X-extent = #'(-0.4 . 0)
    \override SystemStartBar.padding = -0.65
    systemStartDelimiter = #'SystemStartBar
  }
}

\new StaffGroup <<
  { c'1 }
  { c'1 }
>>