Minor tweaks in the main test article

Author: javiereguiluz

testing.rst

@@ -222,7 +222,7 @@ If you need to customize some environment variables for your tests (e.g. the
 ``DATABASE_URL`` used by Doctrine), you can do that by overriding anything you
 need in your ``.env.test`` file:
 
-.. code-block:: text
+.. code-block:: env
 
     # .env.test