[3.12] gh-114552: Update `__dir__` method docs: it allows returning an iterable (GH-114662) (#115234)

gh-114552: Update `__dir__` method docs: it allows returning an iterable (GH-114662)
(cherry picked from commit e19103a346f0277c44a43dfaebad9a5aa468bf1e)

Co-authored-by: Nikita Sobolev <mail@sobolevn.me>