[compiler] Fix ref construction in SFIRef::scope_info

It was missing an AssumeMemoryFence.

Bug: v8:7790,chromium:1236612
Change-Id: Icd3ed9f9979b0ba287c9dff7f4f8722ac06e859a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3073739


Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76110}