Add QT_MODULE(Gui) macro

Fixing `macros' function test of `tst_headers'

Task-number: QTQAINFRA-324
Change-Id: Ib6fcf276108bbb5515a72f3f17b373de82a599fc
Reviewed-by: Olivier Goffart <ogoffart@kde.org>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/widgets/kernel/qplatformdialoghelper_qpa.h

@@ -49,6 +49,8 @@ QT_BEGIN_HEADER
 
 QT_BEGIN_NAMESPACE
 
+QT_MODULE(Gui)
+
 class QString;
 class QObjectPrivate;