[V8] Make archive-branch script Py3 compatible

Bug: v8:13776
Change-Id: I238f819c17c66367b30f7248c52082b409d35a2d
Reviewed-on: https://chromium-review.googlesource.com/c/infra/experimental/+/4288758
Reviewed-by: Alexander Schulze <alexschulze@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
2 files changed