Though the task is never explicitly canceled, making it cancelable
ensures that it is canceled on Isolate teardown.

R=ulan@chromium.org

Bug: v8:8179
Change-Id: Ic3912b7acc7249aed8397010c98dc407222e84be
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2049898Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66250}