[3.13] gh-67206: Document that `string.printable` is not printable in the POSIX sense (GH-128820) (#128868)

gh-67206: Document that `string.printable` is not printable in the POSIX sense (GH-128820)
(cherry picked from commit d906bde250d59c396d8dab92285b832c66cdec27)

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>