qtest.h: actually include qtest_widgets.h

Was including qtest_gui.h instead, for QT_WIDGETS_LIB.

Not a problem in practice, since qtest_widgets.h doesn't
currently add anything on top of qtest_gui.h. But that will
change soon.

Change-Id: I942870cddc7b1ccfda262e2fe26834594336dd0b
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/testlib/qtest.h

@@ -286,7 +286,7 @@ int main(int argc, char *argv[]) \
 
 #if defined(QT_WIDGETS_LIB)
 
-#include <QtTest/qtest_gui.h>
+#include <QtTest/qtest_widgets.h>
 
 #ifdef QT_KEYPAD_NAVIGATION
 #  define QTEST_DISABLE_KEYPAD_NAVIGATION QApplication::setNavigationMode(Qt::NavigationModeNone);