fix(functional-tests): fix test failures on train 287.1 tag

[vpomerleau]

Because

• Some functional tests were failing for the tag

This pull request

• Add assertions in the failing tests

Issue that this pull request solves

Closes: #FXA-9909

Checklist

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• [ ] My commit is GPG signed.
• [ ] If applicable, I have modified or added tests which pass locally.
• [ ] I have added necessary documentation (if appropriate).
• [ ] I have verified that my changes render correctly in RTL (if appropriate).

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[vpomerleau]

I added the fixme in a separate commit without rebasing - in case it has unintended side-effects we can revert.

[vpomerleau]

Tests passed on retry, CI failed on known merge report bug (https://github.com/mozilla/fxa/pull/17146). Going to merge as the failure is unrelated.