test: Fix flaky test "lockdown the UI and background environments are locked down"

[chloeYue]

Description

This PR addresses the flaky 'lockdown' e2e test, specifically when running in Firefox, which is a tricky one.

Root Cause: The flakiness is caused by the rapid execution of the lockdown test script in Firefox immediately after navigating to the BACKGROUND page. This quick transition did not allow sufficient time for the environment to stabilize, preventing the script from accurately assessing the lockdown state.

Fix Implemented: To mitigate this issue, I introduced a await driver.delay(1000) after navigating to the BACKGROUND page and before executing the lockdown test script. This brief pause ensures that the environment is fully loaded and stable, allowing the script to run under consistent conditions and accurately verify the lockdown state.

While I'm agree that the use of delay should be minimized, this test's specific nature and the absence of a way to use the driver to wait for an element's status makes it necessary to use the delay() method.

Results:
Before the Fix: The flakiness could be reproduced locally on Firefox with approximately a 30% occurrence rate.
After the Fix: After implementing the changes, I ran the test 20 consecutive times without encountering any flakiness, demonstrating the effectiveness of the fix.

Related issues

Fixes: #24621

Manual testing steps

1. Run the test several times yarn test:e2e:single test/e2e/tests/request-queuing/ui.spec.js --browser=firefox --leave-running --retryUntilFailure --retries=10
2. Check ci jobs

Screenshots/Recordings

Before

After

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• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
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Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
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[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[metamaskbot]

Builds ready [7a2ff9e]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • ui: 0, 1, 10, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (1360 ± 618 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	76	235	135	46	22
		domContentLoaded	9	87	20	21	10
		load	64	3432	1360	1288	618
		domInteractive	9	87	20	21	10

Bundle size diffs

• background: 0 Bytes (0.00%)
• ui: 0 Bytes (0.00%)
• common: 0 Bytes (0.00%)

[metamaskbot]

Missing release label release-11.16.6 on PR. Adding release label release-11.16.6 on PR and removing other release labels(release-11.18.0), as PR was cherry-picked in branch 11.16.6.