[3.13] gh-121403: Add notes for PyList_GetXXX APIs about the need for init (gh-121626) (gh-121827)

gh-121403: Add notes for PyList_GetXXX APIs about the need for init (gh-121626)
(cherry picked from commit 2bac2b86b1486f15038fb246835e04bb1b213cd8)

Co-authored-by: Donghee Na <donghee.na@python.org>