[turbofan] Fix a rare false positive in SLVerifier

Bug: chromium:1309769, v8:12619
Change-Id: I880c7326f2ec91f1aa985d6b7ed67f8f5afc074b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3548897


Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79608}