Add exception to possible type for the source position table.

Bug: v8:8510
Change-Id: Ia97bba2b88d80ca572be21f236ad85448b6dd6f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1653110
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62087}