Use PEP 585 syntax wherever possible (#6717)

stdlib/_codecs.pyi

@@ -1,13 +1,13 @@
 import codecs
 import sys
-from typing import Any, Callable, Dict, Tuple, Union
+from typing import Any, Callable, Union
 
 # This type is not exposed; it is defined in unicodeobject.c
 class _EncodingMap:
     def size(self) -> int: ...
 
-_MapT = Union[Dict[int, int], _EncodingMap]
-_Handler = Callable[[Exception], Tuple[str, int]]
+_MapT = Union[dict[int, int], _EncodingMap]
+_Handler = Callable[[Exception], tuple[str, int]]
 
 def register(__search_function: Callable[[str], Any]) -> None: ...
 def register_error(__errors: str, __handler: _Handler) -> None: ...