Use Final for undocumented constants (#12450)

stdlib/subprocess.pyi

@@ -2,7 +2,7 @@ import sys
 from _typeshed import ReadableBuffer, StrOrBytesPath
 from collections.abc import Callable, Collection, Iterable, Mapping, Sequence
 from types import TracebackType
-from typing import IO, Any, AnyStr, Generic, Literal, TypeVar, overload
+from typing import IO, Any, AnyStr, Final, Generic, Literal, TypeVar, overload
 from typing_extensions import Self, TypeAlias
 
 if sys.version_info >= (3, 9):
@@ -74,8 +74,8 @@ _T = TypeVar("_T")
 
 # These two are private but documented
 if sys.version_info >= (3, 11):
-    _USE_VFORK: bool
-_USE_POSIX_SPAWN: bool
+    _USE_VFORK: Final[bool]
+_USE_POSIX_SPAWN: Final[bool]
 
 class CompletedProcess(Generic[_T]):
     # morally: _CMD
@@ -1810,9 +1810,9 @@ else:
         text: bool | None = None,
     ) -> Any: ...  # morally: -> str | bytes
 
-PIPE: int
-STDOUT: int
-DEVNULL: int
+PIPE: Final[int]
+STDOUT: Final[int]
+DEVNULL: Final[int]
 
 class SubprocessError(Exception): ...