Board stackup: Ensure that m_choiceCopperLayers is updated

Need to do a full synchronisation with the board to ensure that the
drop down and other UI elements are reset

Fixes https://gitlab.com/kicad/code/kicad/-/issues/9991

pcbnew/board_stackup_manager/panel_board_stackup.cpp

@@ -1239,7 +1239,7 @@ void PANEL_SETUP_BOARD_STACKUP::OnLayersOptionsChanged( LSET aNewLayerSet )
     {
         m_enabledLayers = layersList;
 
-        synchronizeWithBoard( false );
+        synchronizeWithBoard( true );
 
         Layout();
         Refresh();