Update multiprocessing.forkserver to 3.14 (#14174)

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

stdlib/@tests/stubtest_allowlists/py314.txt

@@ -15,7 +15,6 @@ fractions.Fraction.__rpow__
 gzip.GzipFile.readinto
 gzip.GzipFile.readinto1
 gzip.compress
-multiprocessing.forkserver.main
 multiprocessing.managers.BaseListProxy.clear
 multiprocessing.managers.BaseListProxy.copy
 multiprocessing.managers.DictProxy.__ior__

stdlib/multiprocessing/forkserver.pyi

@@ -1,3 +1,4 @@
+import sys
 from _typeshed import FileDescriptorLike, Unused
 from collections.abc import Sequence
 from struct import Struct
@@ -14,13 +15,26 @@ class ForkServer:
     def connect_to_new_process(self, fds: Sequence[int]) -> tuple[int, int]: ...
     def ensure_running(self) -> None: ...
 
-def main(
-    listener_fd: int | None,
-    alive_r: FileDescriptorLike,
-    preload: Sequence[str],
-    main_path: str | None = None,
-    sys_path: Unused = None,
-) -> None: ...
+if sys.version_info >= (3, 14):
+    def main(
+        listener_fd: int | None,
+        alive_r: FileDescriptorLike,
+        preload: Sequence[str],
+        main_path: str | None = None,
+        sys_path: list[str] | None = None,
+        *,
+        authkey_r: int | None = None,
+    ) -> None: ...
+
+else:
+    def main(
+        listener_fd: int | None,
+        alive_r: FileDescriptorLike,
+        preload: Sequence[str],
+        main_path: str | None = None,
+        sys_path: Unused = None,
+    ) -> None: ...
+
 def read_signed(fd: int) -> Any: ...
 def write_signed(fd: int, n: int) -> None: ...