tst_qmenu: fix -Wsuggest-override

... and fix placement of {.

Amends f0049873d2.

Change-Id: I2479087005d350a23e45eda126a89e0be91c0701
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit c41e03008a)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

tests/auto/widgets/widgets/qmenu/tst_qmenu.cpp

@@ -2060,7 +2060,8 @@ void tst_QMenu::nestedTearOffDetached()
     public:
         QMenu *tornOffMenu = nullptr;
     protected:
-        bool eventFilter(QObject *receiver, QEvent *event) {
+        bool eventFilter(QObject *receiver, QEvent *event) override
+        {
             if (event->type() == QEvent::Show && receiver->inherits("QTornOffMenu"))
                 tornOffMenu = qobject_cast<QMenu *>(receiver);
             return QObject::eventFilter(receiver, event);