[3.13] gh-140979: Fix off-by-one error in the RE code validator (GH-140984) (GH-141000)

It was too lenient and allowed MARK opcodes with too large value.
(cherry picked from commit 1326d2a808245e5f2de9e515460bab30556e8f05)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>