design blocks: don't apply nested groups

This could be an improvement in the future, but for now it has too many
issues, e.g. what happens if the user has already grouped those items?

Fixes: https://gitlab.com/kicad/code/kicad/-/work_items/23471

pcbnew/tools/multichannel_tool.cpp

@@ -260,6 +260,10 @@ bool MULTICHANNEL_TOOL::findOtherItemsInRuleArea( RULE_AREA* aRuleArea, std::set
             if( item->Type() == PCB_FOOTPRINT_T )
                 continue;
 
+            // TODO: Preserve nested groups when applying design block layout.
+            if( item->Type() == PCB_GROUP_T )
+                continue;
+
             if( BOARD_ITEM* boardItem = dynamic_cast<BOARD_ITEM*>( item ) )
             {
                 if( !boardItem->IsConnected() || boardItem->Type() == PCB_ZONE_T )