improve readability of phishing page redirect tests

[davidmurdoch]

What is this about?

See #25153 (review) and https://github.com/MetaMask/metamask-extension/pull/25153/files#diff-16a95c1c106d76dcf604b39cf5f6a8a8ccde12e2a8440c7c6db2c223070ac6c1R2 for more context.

In an attempt to make things "better" (subjectively), I actually made things worse (objectively 😅 ).

Perhaps withFixtures should be refactored to be used in its current form, as well as in a form that makes the patterns in this PR less chaotic; maybe a startFixtures function that returns something like Promise<{ driver, <... etc...>, end: () => Promise<void> }> where end could be called by the after/afterAll.

The patterns introduced in the linked PR go against the guidelines in https://github.com/MetaMask/contributor-docs/blob/main/docs/unit-testing.md

And "while you're in there", tackle this function param refactoring as well: #25153 (comment)