QAccessibleWidgetV2: make the dtor protected

QAccessibleWidget (i.e. V1) has a protected dtor, so V2, which merely
extends V1 because we can't add new virtuals (via a new base class)
due to BC constraints, shouldn't differ in this respect.

Amends bb2121551c3d7b1af1553710bc211ba0e39b4212.

Found in API-review.

Pick-to: 6.10
Change-Id: I0c9a00691a14c600b020ff1a9f433634bb7c8d24
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/accessible/qaccessiblewidget.h

@@ -69,8 +69,11 @@ class Q_WIDGETS_EXPORT QAccessibleWidgetV2 : public QAccessibleWidget,
 public:
     explicit QAccessibleWidgetV2(QWidget *object, QAccessible::Role role = QAccessible::Client);
     explicit QAccessibleWidgetV2(QWidget *object, QAccessible::Role role, const QString &name);
+
+protected:
     ~QAccessibleWidgetV2() override;
 
+public:
     void *interface_cast(QAccessible::InterfaceType t) override;
 
     // QAccessibleAttributesInterface