Update expectation in PageLoadMetricsBrowserTest.EarlyHints

`timing.final_response_start_time` and
`timing.final_non_informational_response_start_time` could be
the same.

Bug: 1246479
Change-Id: I77a4fac39d9718ab99707a34093b273a99dfea64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3142374


Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918725}