[3.13] Docs: Fix typo in `os.fwalk()` example (GH-138486) (GH-138501)

Docs: Fix typo in `os.fwalk()` example (GH-138486)
(cherry picked from commit 849a80ec412c36bbca5d400a7db5645b8cf54f1f)

Co-authored-by: William Andrea <22385371+wjandrea@users.noreply.github.com>