Check submission of an app with XSS in it's app name test

This is for issue https://github.com/mozilla/marketplace-tests/issues/488
@AndreiH, is there any reason why you moved the try here, and not before https://github.com/AndreiH/marketplace-tests/blob/xss_issue/tests/desktop/developer_hub/test_developer_hub_submit_apps.py#L287, as we do in our other tests?