Switch to using nbcollection + github actions

[adrn]

Demonstration of switching the execute & convert machinery to nbcollection with github actions instead of custom scripts + circleCI.

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[adrn]

Oops, I think I need to first add a workflow in main to get it to see the new workflow...

[adrn]

Note: there are real failures in the conesearch tutorial because of an issue with the VO server (comments by @pllim in slack). In the long run, we still need to implement a more robust solution for handling remote data. One idea would be to distribute the ~/.astropy/cache needed by the tutorials with this repo so that CI doesn't do any remote data access. In the short term, we might want to just skip the conesearch tutorial in the build process...

[adrn]

@jonathansick I think this is now a working proof of concept! Here is the resulting artifact / zip file of the rendered tutorials: https://github.com/astropy/astropy-tutorials/suites/3848792615/artifacts/95489955
Should we merge this and have you add the cross-deploy in a separate PR?

[adrn]

(Tried to get the circleci error to go away, because I removed the webhook, but no luck...)

[jonathansick]

@adrn This looks great. Since this doesn't affect the current production (afaik), this should be safe to merge now and I'll contribute the cross-deploy into the astropy/learn-astropy repo.

I might need to adjust some of the CSS selectors in astropy/learn-astropy-librarian in order to gather the new notebooks since they aren't wrapped in the Sphinx HTML structure anymore. That shouldn't be an issue, though.

[adrn]

Great! OK I'll do it then - #yolo