Refactor publishing-api assertion
Refactor publishing-api assertion

The current assertion is difficult to read. If we rework this to
block-style it's clearer that we are using the
`be_valid_against_schema` on the second argument to
`#put_content_item`.

alphagov/business-support-finder,alphagov/business-support-finder,alphagov/business-support-finder,alphagov/business-support-finder