Use _typeshed.IdentityFunction more consistently (#8063)

stubs/mypy-extensions/mypy_extensions.pyi

@@ -1,6 +1,6 @@
 import abc
-from _typeshed import Self
-from collections.abc import Callable, ItemsView, KeysView, Mapping, ValuesView
+from _typeshed import IdentityFunction, Self
+from collections.abc import ItemsView, KeysView, Mapping, ValuesView
 from typing import Any, Generic, TypeVar, overload
 
 _T = TypeVar("_T")
@@ -54,6 +54,6 @@ class NoReturn: ...
 # a class decorator, but mypy does not support type[_T] for abstract
 # classes until this issue is resolved, https://github.com/python/mypy/issues/4717.
 def trait(cls: _T) -> _T: ...
-def mypyc_attr(*attrs: str, **kwattrs: object) -> Callable[[_T], _T]: ...
+def mypyc_attr(*attrs: str, **kwattrs: object) -> IdentityFunction: ...
 
 class FlexibleAlias(Generic[_T, _U]): ...

stubs/six/six/__init__.pyi

@@ -3,6 +3,7 @@ from __future__ import print_function
 import builtins
 import types
 import unittest
+from _typeshed import IdentityFunction
 from builtins import next as next
 from collections.abc import Callable, ItemsView, Iterable, Iterator as _Iterator, KeysView, Mapping, ValuesView
 from functools import wraps as wraps
@@ -83,7 +84,7 @@ def raise_from(value: BaseException | type[BaseException], from_value: BaseExcep
 print_ = print
 
 def with_metaclass(meta: type, *bases: type) -> type: ...
-def add_metaclass(metaclass: type) -> Callable[[_T], _T]: ...
+def add_metaclass(metaclass: type) -> IdentityFunction: ...
 def ensure_binary(s: bytes | str, encoding: str = ..., errors: str = ...) -> bytes: ...
 def ensure_str(s: bytes | str, encoding: str = ..., errors: str = ...) -> str: ...
 def ensure_text(s: bytes | str, encoding: str = ..., errors: str = ...) -> str: ...