Do not run test-book-website on main push
This makes little sense to run it again.. we already did run twice on
branch push and for the PR request. And we will run the exact same
thing and more (sans-serif, actual release etc) in release-book-website.
* Validate website format
This validates the format of the website and throws an error if
something is fishy.
* Remove -j flag
* clean build
* Clean cache in between