[3.13] Clarify ast docs to use a less confusing example for `ast.ParamSpec` (GH-127955) (#127959)

Clarify ast docs to use a less confusing example for `ast.ParamSpec` (GH-127955)

Fix typo in ast docs: ParamSpec defaults
(cherry picked from commit 7900a85019457c14e8c6abac532846bc9f26760d)

Co-authored-by: Steve C <diceroll123@gmail.com>