Scxml: use qobject_cast instead of static_cast

Change-Id: Ibcaca17a91856f041fcf9f28c8be6bdc2df63fe6
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/scxmleditor/outputpane/warningmodel.cpp

@@ -239,7 +239,7 @@ Warning *WarningModel::getWarning(const QModelIndex &ind)
 
 void WarningModel::warningDestroyed(QObject *ww)
 {
-    auto w = static_cast<Warning*>(ww);
+    auto w = qobject_cast<Warning*>(ww);
     if (m_warnings.contains(w)) {
         int ind = m_warnings.indexOf(w);
         beginRemoveRows(QModelIndex(), ind, ind);