Fix two unrelated bugs in ungroup.

1) Don't double-remove the members from the group.
2) Don't auto-recurse BOARD_COMMIT::Stage for non-modify
changes.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/16419

pcbnew/board_commit.cpp

@@ -78,13 +78,16 @@ COMMIT& BOARD_COMMIT::Stage( EDA_ITEM* aItem, CHANGE_TYPE aChangeType, BASE_SCRE
 
     // Many operations (move, rotate, etc.) are applied directly to a group's children, so they
     // must be staged as well.
-    if( PCB_GROUP* group = dynamic_cast<PCB_GROUP*>( aItem ) )
+    if( aChangeType == CHT_MODIFY )
     {
-        group->RunOnChildren(
-                [&]( BOARD_ITEM* child )
-                {
-                    Stage( child, aChangeType );
-                } );
+        if( PCB_GROUP* group = dynamic_cast<PCB_GROUP*>( aItem ) )
+        {
+            group->RunOnChildren(
+                    [&]( BOARD_ITEM* child )
+                    {
+                        Stage( child, aChangeType );
+                    } );
+        }
     }
 
     return COMMIT::Stage( aItem, aChangeType );

pcbnew/tools/group_tool.cpp

@@ -311,7 +311,6 @@ int GROUP_TOOL::Ungroup( const TOOL_EVENT& aEvent )
                 toSelect.push_back( member );
             }
 
-            group->GetItems().clear();
             group->SetSelected();
             commit.Remove( group );
         }