Use PEP 585 syntax in Python 2, protobuf & _ast stubs, where possible (#6949)

stdlib/@python2/email/mime/application.pyi

@@ -1,7 +1,7 @@
 from email.mime.nonmultipart import MIMENonMultipart
-from typing import Callable, Optional, Tuple, Union
+from typing import Callable, Optional, Union
 
-_ParamsType = Union[str, None, Tuple[str, Optional[str], str]]
+_ParamsType = Union[str, None, tuple[str, Optional[str], str]]
 
 class MIMEApplication(MIMENonMultipart):
     def __init__(