[3.13] gh-145521: Add 'infer_variance' parameter to ParamSpec class (GH-145522) (#153825)

(cherry picked from commit 2e94f14)

Co-authored-by: Kai (Kazuya Ito) <kazya.ito.dream@gmail.com>

Author: JelleZijlstra

Doc/library/typing.rst

@@ -2051,7 +2051,7 @@ without the dedicated syntax, as documented below.
 
       Support for default values was added.
 
-.. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False, default=typing.NoDefault)
+.. class:: ParamSpec(name, *, bound=None, covariant=False, contravariant=False, infer_variance=False, default=typing.NoDefault)
 
    Parameter specification variable.  A specialized version of
    :ref:`type variables <typevar>`.