FITS-cubes is no longer building in Circle CI

[eblur]

On PR #491 , Circle CI is breaking on the FITS-cubes tutorial:

https://app.circleci.com/pipelines/github/astropy/astropy-tutorials/118/workflows/94aae9e5-44d9-4bd9-aacd-ec7d2ab61920/jobs/801

We need to check if this tutorial can still run locally. If not, the tutorial needs to be fixed. If it can run locally, then there is probably an issue with Circle CI access to the ESA Sky server. We might have to put the required data on the astropy data server instead, and implement a try/except call in the notebook.

This would be a temporary fix to allow new content to be published. At some point in the future, infrastructure will be set up to cache built notebook pages so that adding a new notebook and building the website will not require running EVERY notebook every time.

[adrn]

Going to close this because the build machinery is about to change, and I've already disabled the circleci builds! (see #495)