[3.14] pythongh-142067: Add missing default value for param in multiprocessing.Pipe's doc (pythonGH-142109) (python#142120)

pythongh-142067: Add missing default value for param in `multiprocessing.Pipe`'s doc (pythonGH-142109)
(cherry picked from commit 229ed3d)

Co-authored-by: flovent <flbven@protonmail.com>

Author: miss-islington

Doc/library/multiprocessing.rst

@@ -890,7 +890,7 @@ For an example of the usage of queues for interprocess communication see
 :ref:`multiprocessing-examples`.
 
 
-.. function:: Pipe([duplex])
+.. function:: Pipe(duplex=True)
 
    Returns a pair ``(conn1, conn2)`` of
    :class:`~multiprocessing.connection.Connection` objects representing the