`DateTimeControl` doesn't render Validation Error Message

[jakubboucek]

DateTimeControl doesn't render Validation Error Message.

When is added Error message for this Control, it is not visible in rendered HTML.

        $form = new BootstrapForm();
        $form->addDate('date', 'Datum');
        $form->onValidate[] = function (Form $form): void {
                $form['date']->addError('Foobar error message');
        };

Nothing rendered:

[dakorpar]

Hi, can you prepare PR?