[wdspec] Update script invalid tests to properly check invalid optional arguments
Depends on D216811
In most cases, the calls would fail early because of a missing channel argument.
Ideally for invalid tests, all the payload should be correct except for the invalid argument we are testing.
Differential Revision: https://phabricator.services.mozilla.com/D216865
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1908621
gecko-commit: f0952d56d427b2f8bd8e03576403aef0a650f8d2
gecko-reviewers: webdriver-reviewers, whimboo