[3.12] gh-105184: document that marshal functions can fail and need to be checked with PyErr_Occurred (GH-105185) (#105218)

gh-105184: document that marshal functions can fail and need to be checked with PyErr_Occurred (GH-105185)
(cherry picked from commit ee26ca13a129da8cf549409d0a1b2e892ff2b4ec)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>