missing annotation and fix warning

Author: 3nids

python/core/layertree/qgslayertree.sip

@@ -143,7 +143,7 @@ class QgsLayerTree : QgsLayerTreeGroup
 
     virtual void writeXml( QDomElement &parentElement );
 
-    virtual QgsLayerTree *clone() const;
+    virtual QgsLayerTree *clone() const /Factory/;
 
     void clear();
 %Docstring

src/core/layertree/qgslayertree.h

@@ -183,7 +183,7 @@ class CORE_EXPORT QgsLayerTree : public QgsLayerTreeGroup
 
     virtual void writeXml( QDomElement &parentElement ) override;
 
-    virtual QgsLayerTree *clone() const override;
+    virtual QgsLayerTree *clone() const override SIP_FACTORY;
 
     /**
      * Clear any information from this layer tree.