In Oilpan minor GCs we don't trace the V8 subgraph. The commit
2da23bd5 broke it for the concurrent marker case. This CL bails
out from visiting TracedReferences in the concurrent marker visitor,
same as what we do for the mutator marking visitor.

Bug: chromium:1029379
Change-Id: Iabeba11fd3d030e9dc5961a364481a0a7d8b8245
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3602520Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80135}