minor #5701 Update testing.rst (hansallis)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes #5701).

Discussion
----------

Update testing.rst

Fixed a grammar error

Commits
-------

2f89488 Update testing.rst

cookbook/email/testing.rst

@@ -31,7 +31,7 @@ Start with an easy controller action that sends an email::
     Don't forget to enable the profiler as explained in :doc:`/cookbook/testing/profiling`.
 
 In your functional test, use the ``swiftmailer`` collector on the profiler
-to get information about the messages send on the previous request::
+to get information about the messages sent on the previous request::
 
     // src/AppBundle/Tests/Controller/MailControllerTest.php
     use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;