Drive-by: Use only LocalIsolate in AllocateConcurrentSP

Bug: v8:12054
Change-Id: Ibdd8b562548f249fc2be4dca723ce4fedc7c09ad
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3240783
Auto-Submit: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77520}