Fix various ParamSpec errors in typing (GH-24176)

1. ParamSpec -> TypeVar for ``typing.Concatenate``
2. ParamSpec's call signature should align with its documentation.
Noticed in GH-24169

Doc/library/typing.rst

@@ -695,10 +695,10 @@ These can be used as types in annotations using ``[]``, each having a unique syn
 
       from collections.abc import Callable
       from threading import Lock
-      from typing import Any, Concatenate, ParamSpec
+      from typing import Any, Concatenate, ParamSpec, TypeVar
 
       P = ParamSpec('P')
-      R = ParamSpec('R')
+      R = TypeVar('R')
 
       # Use this lock to ensure that only one thread is executing a function
       # at any time.

Lib/typing.py

@@ -779,7 +779,7 @@ def add_two(x: float, y: float) -> float:
     args = object()
     kwargs = object()
 
-    def __init__(self, name, bound=None, covariant=False, contravariant=False):
+    def __init__(self, name, *, bound=None, covariant=False, contravariant=False):
         self.__name__ = name
         super().__init__(bound, covariant, contravariant)
         try: