minor #7235 Misused "tag" for "tags" (b0nd0)

This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes #7235).

Discussion
----------

Misused "tag" for "tags"

"tag" used in code, while "tags" used in description

Commits
-------

59eec4c Misused "tag" for "tags"

Author: xabbuh

testing.rst

@@ -725,8 +725,8 @@ add the values to the raw data array::
     $values = $form->getPhpValues();
 
     // Add fields to the raw values.
-    $values['task']['tag'][0]['name'] = 'foo';
-    $values['task']['tag'][1]['name'] = 'bar';
+    $values['task']['tags'][0]['name'] = 'foo';
+    $values['task']['tags'][1]['name'] = 'bar';
 
     // Submit the form with the existing and new values.
     $crawler = $this->client->request($form->getMethod(), $form->getUri(), $values,