Use PEP 604 syntax wherever possible, part II (#7514)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

stdlib/smtplib.pyi

@@ -4,7 +4,7 @@ from email.message import Message as _Message
 from socket import socket
 from ssl import SSLContext
 from types import TracebackType
-from typing import Any, Pattern, Protocol, Sequence, Union, overload
+from typing import Any, Pattern, Protocol, Sequence, overload
 
 if sys.version_info >= (3, 7):
     __all__ = [
@@ -43,7 +43,7 @@ else:
 _Reply = tuple[int, bytes]
 _SendErrs = dict[str, _Reply]
 # Should match source_address for socket.create_connection
-_SourceAddress = tuple[Union[bytearray, bytes, str], int]
+_SourceAddress = tuple[bytearray | bytes | str, int]
 
 SMTP_PORT: int
 SMTP_SSL_PORT: int