Format strings are the convention in Py3

R=machenbach@chromium.org,alexschulze@chromium.org

Bug: chromium:1298869
Change-Id: Ia660e933f07d2a592c2edadaa99df68c47adb80d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3521789
Auto-Submit: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79477}