Fix lacks of Q_OBJECT macro

Change-Id: I0de19ed983c45260c957ea88422093bf7faca6a1
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/scxmleditor/plugin_interface/scattributeitemmodel.h

@@ -33,6 +33,7 @@ namespace PluginInterface {
 
 class SCAttributeItemModel : public AttributeItemModel
 {
+    Q_OBJECT
 public:
     SCAttributeItemModel(QObject *parent = nullptr);