Add layout in QRadioButton baseline test for better visualization

Task-number: QTBUG-99749
Pick-to: 6.3
Change-Id: Iafd097d42b312cc24a60107c00e9c52fc0f3cdff
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

tests/baseline/widgets/tst_baseline_widgets.cpp

@@ -354,6 +354,7 @@ void tst_Widgets::tst_QRadioButton()
     QBoxLayout box(QBoxLayout::TopToBottom);
     box.addWidget(&button1);
     box.addWidget(&button2);
+    testWindow()->setLayout(&box);
     takeStandardSnapshots();
 
     const QPoint clickTarget = button1.rect().center();