fix type for multiprocessing.log_to_stderr(): allow int level (#9334)

Co-authored-by: AlexWaygood <alex.waygood@gmail.com>

stdlib/multiprocessing/util.pyi

@@ -1,7 +1,7 @@
 import threading
 from _typeshed import Incomplete, ReadableBuffer, SupportsTrunc
 from collections.abc import Callable, Iterable, Mapping, MutableMapping, Sequence
-from logging import Logger
+from logging import Logger, _Level as _LoggingLevel
 from typing import Any, SupportsInt
 from typing_extensions import SupportsIndex
 
@@ -37,7 +37,7 @@ def debug(msg: object, *args: object) -> None: ...
 def info(msg: object, *args: object) -> None: ...
 def sub_warning(msg: object, *args: object) -> None: ...
 def get_logger() -> Logger: ...
-def log_to_stderr(level: int | None = ...) -> Logger: ...
+def log_to_stderr(level: _LoggingLevel | None = ...) -> Logger: ...
 def is_abstract_socket_namespace(address: str | bytes | None) -> bool: ...
 
 abstract_sockets_supported: bool