tst_qmllint: Fix requiredProperty.qml test

The clean example for testing required properties was using the root
component which we do not check for required property errors, use
inline components instead.

Pick-to: 6.2
Change-Id: I945ed5c15334b7d88161dddd27b6962593184f9e
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

tests/auto/qml/qmllint/data/requiredProperty.qml

@@ -1,7 +1,9 @@
-import QtQml 2.15
+import QtQuick 2.15
 
-QtObject {
-    property int x
-    required x
-    x: 5
+Item {
+    component Required : QtObject {
+        property int x
+        required x
+    }
+    Required { x: 5 }
 }