Resolve title variable when plotting

Be sure to use variable name if it exists when plotting the file

Fixes https://gitlab.com/kicad/code/kicad/issues/11608

(cherry picked from commit d971cbefcb)

eeschema/dialogs/dialog_plot_schematic.cpp

@@ -804,7 +804,7 @@ void DIALOG_PLOT_SCHEMATIC::createPDFFile( bool aPlotAll, bool aPlotDrawingSheet
     plotter->SetRenderSettings( aRenderSettings );
     plotter->SetColorMode( getModeColor() );
     plotter->SetCreator( wxT( "Eeschema-PDF" ) );
-    plotter->SetTitle( m_parent->GetTitleBlock().GetTitle() );
+    plotter->SetTitle( ExpandTextVars( m_parent->GetTitleBlock().GetTitle(), &m_parent->Prj() ) );
 
     wxString   msg;
     wxFileName plotFileName;