Dropping the gpu:none dimension broadens the choice of Mac bots from
so far only 8-core VMs to also include 4-core and 12-core Mac Minis.

This CL adjusts the shard configs to account for adding
4-core Mac Minis to the choice.

We also skip a test that's slow only on 4-core bots.

No-Try: true
Bug: chromium:1174040,v8:11418
Change-Id: Ic0be0db197341b7b8f88eb30aa284c38b0e69609
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2685164
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72623}