Add chrome-cherry-picker to known robots list.

Add the chrome-cherry-picker service account email to KNOWN_ROBOTS so
the presubmits don't think that this is an external account trying to
commit to src.
Security review bug: https://b.corp.google.com/issues/403244734

Change-Id: I8dad3157cc944a056433f12460afbecbdcb10757
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6425146
Reviewed-by: Daniel Yip <danielyip@google.com>
Commit-Queue: Gennady Tsitovich <gtsitovich@google.com>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1441793}