bpo-30668: add missing word in license.rst (GH-13115)

(cherry picked from commit 4920c09)

Co-authored-by: Patrick Mühlbauer <tmuxbiene@googlemail.com>

Author: miss-islington

Doc/license.rst

@@ -561,7 +561,7 @@ SipHash24
 ---------
 
 The file :file:`Python/pyhash.c` contains Marek Majkowski' implementation of
-Dan Bernstein's SipHash24 algorithm. The contains the following note::
+Dan Bernstein's SipHash24 algorithm. It contains the following note::
 
   <MIT License>
   Copyright (c) 2013  Marek Majkowski <marek@popcount.org>