[3.11] Fix rendering of null character in ast.rst (GH-116080) (#116161)

Fix rendering of null character in ast.rst (GH-116080)
(cherry picked from commit c04a981ff414b101736688773dbe24f824ca32ce)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>