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

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

Fix typo in ast docs: ParamSpec defaults
(cherry picked from commit 7900a85)

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

Author: miss-islington

Doc/library/ast.rst

@@ -1802,15 +1802,15 @@ aliases.
 
    .. doctest::
 
-        >>> print(ast.dump(ast.parse("type Alias[**P = (int, str)] = Callable[P, int]"), indent=4))
+        >>> print(ast.dump(ast.parse("type Alias[**P = [int, str]] = Callable[P, int]"), indent=4))
         Module(
             body=[
                 TypeAlias(
                     name=Name(id='Alias', ctx=Store()),
                     type_params=[
                         ParamSpec(
                             name='P',
-                            default_value=Tuple(
+                            default_value=List(
                                 elts=[
                                     Name(id='int', ctx=Load()),
                                     Name(id='str', ctx=Load())],