[imaplib] IMAP4.append returns a tuple (status, [data]) (#15183)

Author: savanto

stdlib/imaplib.pyi

@@ -61,7 +61,7 @@ class IMAP4:
     def socket(self) -> _socket: ...
     def recent(self) -> _CommandResults: ...
     def response(self, code: str) -> _CommandResults: ...
-    def append(self, mailbox: str, flags: str, date_time: str, message: ReadableBuffer) -> str: ...
+    def append(self, mailbox: str, flags: str, date_time: str, message: ReadableBuffer) -> tuple[str, _list[bytes]]: ...
     def authenticate(self, mechanism: str, authobject: Callable[[bytes], bytes | None]) -> tuple[str, str]: ...
     def capability(self) -> _CommandResults: ...
     def check(self) -> _CommandResults: ...