Fix flaky TranslateManagerBackForwardCacheBrowserTest.

Bug: 331926163
Change-Id: Id99fe22a7518d4109e67a7ae0e3f925bde042e83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5428410


Reviewed-by: Trevor Perrier <perrier@chromium.org>
Reviewed-by: Anthony Cui <cuianthony@chromium.org>
Commit-Queue: Anthony Cui <cuianthony@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283473}