We never knew why they broke on CI last time and not on any of
machines.. checking if that was a setup issue on github side. This
woudl enable much faster builds.
This temporarily removes the parallel option from make to ensure that we
can release the booklet. I am not sure why it causes an issue. Baking
the book without it causes no problem.
* 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