Add os.setns for Linux on Python 3.12+ (#10789)

stdlib/os/__init__.pyi

@@ -1101,3 +1101,4 @@ if sys.version_info >= (3, 12) and sys.platform == "linux":
     CLONE_THREAD: int
     CLONE_VM: int
     def unshare(flags: int) -> None: ...
+    def setns(fd: FileDescriptorLike, nstype: int = 0) -> None: ...

stdlib/posix.pyi

@@ -344,6 +344,7 @@ if sys.platform != "win32":
             CLONE_SYSVSEM as CLONE_SYSVSEM,
             CLONE_THREAD as CLONE_THREAD,
             CLONE_VM as CLONE_VM,
+            setns as setns,
             unshare as unshare,
         )