Correct typo in typing.py (GH-100423)

In the docstring of `ParamSpec`, the name of `P = ParamSpec('P')` was
mistakenly written as `'T'`.
(cherry picked from commit 6898157)

Co-authored-by: david-why <david_why@outlook.com>

Author: miss-islington

Lib/typing.py

@@ -901,7 +901,7 @@ def add_two(x: float, y: float) -> float:
 
     Parameter specification variables can be introspected. e.g.:
 
-       P.__name__ == 'T'
+       P.__name__ == 'P'
        P.__bound__ == None
        P.__covariant__ == False
        P.__contravariant__ == False