qtquick: Fix a test

The tests are not prepared for the min-size of the floating window
to change (QLayout helped with that). We need to write some kind
of constraint propagation first, until then we use a static
size for the non-contents

examples/qtquick/customtitlebar/MyTitleBar.qml

@@ -19,7 +19,7 @@ KDDW.TitleBarBase {
     color: "black"
     border.color: "orange"
     border.width: 2
-    height: visible ? 50 : 0
+    heightWhenVisible: 50
 
     Text {
         color: "orange"