Fix 'the the' duplication (partial backport of r71103
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index df2cd8f..f6e223a 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -1845,7 +1845,7 @@
 any :class:`~multiprocessing.Process` object that the current process creates.
 This means that (by default) all processes of a multi-process program will share
 a single authentication key which can be used when setting up connections
-between the themselves.
+between themselves.
 
 Suitable authentication keys can also be generated by using :func:`os.urandom`.