add missing type_check_only import

Co-authored-by: Sebastian Rittau <sebastian.rittau@zfutura.de>

Author: hoel-bagard

stubs/tensorflow/tensorflow/keras/metrics.pyi

@@ -2,7 +2,7 @@ from _typeshed import Incomplete
 from abc import ABCMeta, abstractmethod
 from collections.abc import Callable, Iterable, Sequence
 from enum import Enum
-from typing import Any, Literal
+from typing import Any, Literal, type_check_only
 from typing_extensions import Self, TypeAlias
 
 import tensorflow as tf