ThinStrings are not transitioned to other string representations, so we
shouldn't need the snapshotting protocol for them.

Change-Id: I17cee1a4171b10c441a005ac29bd232a0a065207
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3852489Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82727}