Investigate our website building with GitHub Actions

[pniedzielski]

https://github.blog/news-insights/product-news/github-pages-now-uses-actions-by-default/

It looks like we build our website with GitHub Actions now, but there may be some incompatibility:

Bundler can't satisfy your Gemfile's dependencies.
Install missing gems with bundle install.
Warning: The github-pages gem can't satisfy your Gemfile's dependencies. If you want to use a different Jekyll version or need additional dependencies, consider building Jekyll site with GitHub Actions: https://jekyllrb.com/docs/continuous-integration/github-actions/
To use retry middleware with Faraday v2.0+, install faraday-retry gem

It looks like the page builds fine, though.