[PR #8286/28f1fd88 backport][3.10] docs: remove repetitive word in co…

…mment (#8288)

**This is a backport of PR #8286 as merged into master
(28f1fd8).**

Co-authored-by: crazehang <165746307+crazehang@users.noreply.github.com>

docs/testing.rst

@@ -775,7 +775,7 @@ Utilities
       mocked.assert_called_with(1, 2)
 
 
-  :param return_value: A value that the the mock object will return when
+  :param return_value: A value that the mock object will return when
       called.
   :returns: A mock object that behaves as a coroutine which returns
       *return_value* when called.