When GC triggered while an exception is pending, a read to
memory that was no longer valid could happen while backtracking in the
regexp interpreter (introduced with commit fb0df2c8).
This CL prevents this dirty read, that could have been a security issue.

Bug: chromium:992389, v8:9575
Change-Id: Ie1acd6faa16665e211666c6a8dcf2a9d74e0c886
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1751342
Commit-Queue: Patrick Thier <pthier@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63195}