pcbnew, export to STEP: fix error in command line tolerance option (--min-distance="0.0100 mm") is some countries

In countries using a comma as floating point separator, the --min-distance="0.0100 mm" was passed as --min-distance="0,0100 mm"
This is incorrect and broke the command line.

Fixes: lp:1814559
https://bugs.launchpad.net/kicad/+bug/1814559

pcbnew/dialogs/dialog_export_step.cpp

@@ -317,6 +317,7 @@ void DIALOG_EXPORT_STEP::onExportButton( wxCommandEvent& aEvent )
 
     if( m_tolerance->GetSelection() != 1 )
     {
+        LOCALE_IO dummy;
         double tolerance = 0.001 * std::pow<double>( 10.0, m_tolerance->GetSelection() - 1 );
         cmdK2S.Append( wxString::Format( " --min-distance=\"%.4f mm\"", tolerance ) );
     }