Update multiprocessing module for 3.14 (#14114)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

stdlib/@tests/stubtest_allowlists/darwin-py314.txt

@@ -10,8 +10,6 @@ asyncio.unix_events._DefaultEventLoopPolicy
 ctypes.c_double_complex._type_
 ctypes.c_float_complex._type_
 ctypes.c_longdouble_complex._type_
-multiprocessing.popen_fork.Popen.interrupt
-multiprocessing.reduction.ACKNOWLEDGE
 
 
 # =======

stdlib/@tests/stubtest_allowlists/linux-py314.txt

@@ -11,6 +11,4 @@ ctypes.c_double_complex._type_
 ctypes.c_float_complex._type_
 ctypes.c_longdouble_complex._type_
 errno.EHWPOISON
-multiprocessing.popen_fork.Popen.interrupt
-multiprocessing.reduction.ACKNOWLEDGE
 select.EPOLLWAKEUP

stdlib/multiprocessing/popen_fork.pyi

@@ -18,6 +18,9 @@ if sys.platform != "win32":
         def duplicate_for_child(self, fd: int) -> int: ...
         def poll(self, flag: int = 1) -> int | None: ...
         def wait(self, timeout: float | None = None) -> int | None: ...
+        if sys.version_info >= (3, 14):
+            def interrupt(self) -> None: ...
+
         def terminate(self) -> None: ...
         def kill(self) -> None: ...
         def close(self) -> None: ...

stdlib/multiprocessing/reduction.pyi

@@ -43,7 +43,8 @@ if sys.platform == "win32":
         def detach(self) -> int: ...
 
 else:
-    ACKNOWLEDGE: Final[bool]
+    if sys.version_info < (3, 14):
+        ACKNOWLEDGE: Final[bool]
 
     def recvfds(sock: socket, size: int) -> list[int]: ...
     def send_handle(conn: HasFileno, handle: int, destination_pid: Unused) -> None: ...