[3.13] Fix documentation of hash in PyHash_FuncDef (GH-137595) (#137643)

Fix documentation of hash in PyHash_FuncDef (GH-137595)

Because of a small typo, it wasn't showing up in the generated docs.
(cherry picked from commit 70218b40082396d68c277667fc9bb7f87d095e3c)

Co-authored-by: da-woods <dw-git@d-woods.co.uk>