[3.12] gh-126055: Add omitted command (in docs [os.walk]) for code to fulfill `shutil.rmtree` algorithm (GH-126067) (GH-126200)

gh-126055:  Add omitted command (in docs [os.walk]) for code to fulfill `shutil.rmtree` algorithm (GH-126067)

* gh-126055:  Add omitted command (in docs [os.walk]) for code to fulfill `shutil.rmtree` algorithm.

Resolves GH-126055

* gh-126055:  Fix omitted code highlighting
(cherry picked from commit 597d814334742dde386a4d2979b9418aee6fcaba)

Co-authored-by: Victor Wheeler <vwheeler63@users.noreply.github.com>