Update api-cache test to be more stable when running quickly

[aaemnnosttv]

Summary

Addresses issue:

• Fix flaky E2E tests #8229

Relevant technical choices

This PR only addresses the one failure we are seeing in the changes to api-cache test where the time value was not greater than before. The change here ensures that even if the test runs the assertions within the same second that the latter value should always be greater than the first. If it fails again, then there may be a real issue with the cache or storage prefix.

Also modified a JS test to fix an unrelated instability. See /~https://github.com/google/site-kit-wp/actions/runs/12915141223/job/36016312697?pr=10103

PR Author Checklist

• My code is tested and passes existing unit tests.
• My code has an appropriate set of unit tests which all pass.
• My code is backward-compatible with WordPress 5.2 and PHP 7.4.
• My code follows the WordPress coding standards.
• My code has proper inline documentation.
• I have added a QA Brief on the issue linked above.
• I have signed the Contributor License Agreement (see https://cla.developers.google.com/).

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Code Reviewer Checklist

• Run the code.
• Ensure the acceptance criteria are satisfied.
• Reassess the implementation with the IB.
• Ensure no unrelated changes are included.
• Ensure CI checks pass.
• Check Storybook where applicable.
• Ensure there is a QA Brief.
• Ensure there are no unexpected significant changes to file sizes.

Merge Reviewer Checklist

• Ensure the PR has the correct target branch.
• Double-check that the PR is okay to be merged.
• Ensure the corresponding issue has a ZenHub release assigned.
• Add a changelog message to the issue.

[aaemnnosttv]

Not related to E2E obviously but another instability which failed here that this should fix.

See /~https://github.com/google/site-kit-wp/actions/runs/12915141223/job/36016312697?pr=10103