When a GC was requested via stack guard, we don't restart incremental
marking anymore on finding new objects but rather finish the GC cycle.

This regressed in https://crrev.com/c/3702801

Bug: v8:12985, chromium:1338071, v8:12775
Change-Id: Ie515cea6d5345ad1111a4fb9f042cffc52083453
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3716486Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81291}