ScxmlEditor: Fix build with Qt5.15

Amends 8b444f88eb.

Change-Id: Ide1da6a6c26f3a72388b2f9642ae25ce3cf62171
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/scxmleditor/plugin_interface/sceneutils.cpp

@@ -317,7 +317,7 @@ void layout(const QList<QGraphicsItem*> &items)
         }
 
         // Finally set initial and final positions
-        for (const ConnectableItem *item : qAsConst(childItems)) {
+        for (ConnectableItem *item : qAsConst(childItems)) {
             if (item == firstItem)
                 initialItem->setPos(firstItem->pos() + firstItem->boundingRect().topLeft()
                                     - QPointF(50, 50));