This is a reland of dcd91455

This CL fixes two more tests that were uncovered by the
non-concurrent marking bot.

Original change's description:
> [heap] Do not scan main thread handles when starting marking
>
> We do not need to scan main thread handles when starting incremental
> marking. This reduces the time to start incremental marking.
>
> Bug: v8:11645
> Change-Id: Ib99a13e7875f50fbfe5346ac0e186d8960ea1337
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2826124
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#73994}

Bug: v8:11645
Change-Id: Id5b9dd0dcec08b6888a885b4f02783f674af90fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2831879Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74029}