This will allow to distinguish between the standard runner and the num fuzzer
on the infra side when generating flako command lines. The value could be
inferred, but it'd be more confusing.

Bug: v8:8971
Change-Id: I78f5104135d1c7fd7d98bceb4b17897e79421455
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1564050
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60769}