csuite.py compare command currently throws exception

"_csv.Error: iterator should return strings, not bytes
(did you open the file in text mode?)"

This should fix it.

Change-Id: I69c0ec43575a8c3627dac81dc99e47ba6adf6f61
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2316833Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#69050}