This means that we are now background serializing
RefSerializationKind::kBackgroundSerialized classes on all configs.

Bug: v8:7790
Change-Id: Iaa54718303e07e37a95d3f54d0c4c173d4174967
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3056453Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75952}