Fix build warnings due to differing virtual method signatures

Author: nyalldawson

src/app/dwg/qgsdwgimporter.h

@@ -57,7 +57,7 @@ class QgsDwgImporter : public DRW_Interface
 
     void addBlock( const DRW_Block &data ) override;
 
-    void setBlock( int handle ) override;
+    void setBlock( const int handle ) override;
 
     //! Called to end the current block
     void endBlock() override;

src/app/qgsattributesformproperties.h

@@ -268,7 +268,7 @@ class DnDTree : public QTreeWidget
     // QTreeWidget interface
   protected:
     QStringList mimeTypes() const override;
-    QMimeData *mimeData( QList<QTreeWidgetItem *> items ) const override;
+    QMimeData *mimeData( const QList<QTreeWidgetItem *> items ) const override;
 
 
   private slots: