This fixes a bug when an encoded character appears in the difference
string. Python3 doesn't require any encoding.

TBR=tmrts@chromium.org

No-Try: true
Bug: chromium:1095964
Change-Id: I49c66b5b9c105ad64d3a7839d0eb5df97ff5f404
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2249660Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68384}