Fix Flaky Phishing Detection Integration Tests

[not-a-rootkit]

Task/Issue URL: https://app.asana.com/0/0/1208253815417569/f
Tech Design URL:
CC:

Description:
Although the tests passed reliably locally, they are currently flaky in CI, due to the timeouts in waitForPageToLoad. Instead we introduce the same pattern we use for PrivacyDashboard and other ErrorPage tests:

let isPhishingPromise = tab.privacyInfoPublisher
    .compactMap { $0?.$isPhishing }
    .map { _ in expectedIsPhishing }
    .timeout(10)
    .first()
    .promise()
let navigationFailedPromise = tab.$error.compactMap { $0 }.timeout(5).first().promise()

This allows us to not have to wait for particular navigation events, but instead wait for changes in internal state, which should be significantly more reliable.

Steps to test this PR:

1. Run PhishingDetectionIntegrationTests.
2. Ensure they all pass reliably.

Definition of Done:

• Does this PR satisfy our Definition of Done?

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