Use Self as the return type for email.policy.Policy.clone (#10301)

Signed-off-by: oleg.hoefling <[email protected]>

Author: hoefling

stdlib/email/policy.pyi

@@ -5,6 +5,7 @@ from email.errors import MessageDefect
 from email.header import Header
 from email.message import Message
 from typing import Any
+from typing_extensions import Self
 
 __all__ = ["Compat32", "compat32", "Policy", "EmailPolicy", "default", "strict", "SMTP", "HTTP"]
 
@@ -25,7 +26,7 @@ class Policy(metaclass=ABCMeta):
         mangle_from_: bool = ...,
         message_factory: Callable[[Policy], Message] | None = ...,
     ) -> None: ...
-    def clone(self, **kw: Any) -> Policy: ...
+    def clone(self, **kw: Any) -> Self: ...
     def handle_defect(self, obj: Message, defect: MessageDefect) -> None: ...
     def register_defect(self, obj: Message, defect: MessageDefect) -> None: ...
     def header_max_count(self, name: str) -> int | None: ...