Refactor security config spec to use mountExtended

FYI - I think extendedWrapper was introduced first and mountExtended was added at a later point, but it seems to be the way-to-go now: https://docs.gitlab.com/ee/development/testing_guide/frontend_testing.html#how-to-query-dom-elements

Also switching over to mountExtended will require some additional changes.

It should be just a of replacing the extendWrapper(mount(... call. When trying it out locally it seemed to work, but I might be missing something 🤔