Also bump shards on a slow builder.

No-Try: true
Bug: v8:13074
Change-Id: I07131c53d1d632886039e811de38961dd4eb5752
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3760458Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81716}