Get CI to check if demo artwork renders successfully

[Keavon]

We want CI to guard against breaking the renderability of the demo artwork.

@TrueDoctor how easy is this?

[TrueDoctor]

We should be able to just add a unit test for this right?

[Keavon]

Yes, that was what I meant by CI (unit tests checked by CI).

[TrueDoctor]

In that case pretty easy

[Keavon]

Feel free to add a test for this when you get a little spare time then! It would be valuable in the short-term to help us avoid mistakes. It just needs to ensure the actual graph renders real output.