Fix CBVTest example code block indentation

[grahamu]

Two code block examples are not recognized as code blocks because they have two levels of indent:

This PR should fix that formatting by removing one level of indent. Although I haven't seen the result rendered locally (just on github, "View file"), I'm following the same convention seen in the rest of DTP documentation, one level of indent.

I didn't add the ReST code-block syntax since the existing DTP documentation does not use that format.

..  code-block:: php

The result:

[jefftriplett]

@grahamu thank you for the contribution!