[3.11] Fix typo in multiprocessing docs (GH-115650) (#115680)

(cherry picked from commit 57d31ec)

Co-authored-by: Naglis Jonaitis <827324+naglis@users.noreply.github.com>

Author: miss-islington

Doc/library/multiprocessing.rst

@@ -2938,7 +2938,7 @@ Beware of replacing :data:`sys.stdin` with a "file like object"
 The *spawn* and *forkserver* start methods
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-There are a few extra restriction which don't apply to the *fork*
+There are a few extra restrictions which don't apply to the *fork*
 start method.
 
 More picklability