[3.13] gh-106318: Add examples for str.rindex() method (GH-143887) (#144422)

gh-106318: Add examples for str.rindex() method (GH-143887)
(cherry picked from commit 45d00a0791a53f07c0050b985c936281ed825d9b)

Co-authored-by: Adorilson Bezerra <adorilson@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>