Fix broken inclusion of webenigne spellcheck test

Change 33e20b47

 switched no_spellchecker into use_spellchecker,
however change for tests directory was incorrect.

Task-number: QTBUG-59687
Change-Id: Ie4d4dae863b90a3b35c9e92c88332096aad75325
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>