gh-pages should not rebase in CI about nimibook

[pietroppeter]

not sure how exactly it works and if this fixes our isse, but this action seems interesting: https://github.com/peaceiris/actions-gh-pages#%EF%B8%8F-use-the-latest-and-specific-release

[pietroppeter]

the action above seems to work fine (see f6e402d), although it changes completely how gh-pages branch looks like (it contains only the docs folder). problem, it still contains some stuff from from the docs folder that should not be there: https://pietroppeter.github.io/nimibook/misc/but/very/far/contributors.html

I can try removing gh-pages and launching CI again?

[pietroppeter]

ok, done some tests on adding and removing a file and all seems to work fine. Pages setup need to change to use gh-pages branches with root folder. When deleting gh-pages this setup needs to be done again