ci: build docs with new Ruby deployment

[henryiii]

See readthedocs/readthedocs.org#10346.

[henryiii]

@MSanKeys963, this now builds in <1 minute with the new native Ruby support on ReadTheDocs! 🎉

@stefanv or @jarrodmillman, we still don't get the nice PR integration, ReadTheDocs says:

Warning

Could not send GitHub build status report for "scientific-python-cookie". Make sure you have the correct GitHub repository permissions and your GitHub account is connected to Read the Docs.

Could not send GitHub build status report for "repo-review". Make sure you have the correct GitHub repository permissions and your GitHub account is connected to Read the Docs.

I've manually set the web hook, so it does build, it just doesn't update the PR with the link in the checks list.

[stefanv]

@henryiii I signed into RTD and gave it permissions, so hopefully it works now. But let me know if I need to do anything else.

[henryiii]

Working, thanks!