CI: there should be a devdeps job for html building

[bsipocz]

The job should pick up upcoming myst changes, such as this one: jupyter-book/mystmd#2387

I think it should be sufficient if we were to run it from cron, and it should be enough to run execution on only one or a small sample of notebooks.

Another thing to consider is to pin the myst versions for deployment and use dependabot to pick up updates, then those update PRs could serve for checking for changes. I really don't like pinning versions, but this case it would be for the docs deployment and I don't think we expect anyone to be able to build the site besides ourselves.

[bsipocz]

@troyraen - this should go on the todo list, eg. I know that there some stuff coming in the next release that will break, it's something super easy to fix right after the release, but also going fwd it would be good to be knowing it ahead of time.

[troyraen]

Thanks, and feel free to add things there yourself.