Also mark a slow test for better throughput.

No-Try: true
Change-Id: Ib8520ba3d00328cc27f330aff594b57d33ebe88d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1981502Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65572}