Gracefully handle unfound attributes

[Jameskmonger]

If there is no expected or actual attribute in the TAP details, they are displayed as undefined.

I think that generally to comply with the TAP specification, if either expected and actual are not found in the YAML output, you should instead render the output directly as raw YAML.

Here is the output which causes the above screenshot:

# failing test
not ok 66 notEqual: [5]
  ---
    forbidden: 5
  ...