ci: Fix jekyll-build-pages source for https://ocaml-sf.org/learn-ocaml/

[erikmd]

• Kind: bugfix

• Follows-up: Deploy artifacts to github-pages #576

Description

the merge of #576 slightly broke the deployment of the regular website on https://ocaml-sf.org/learn-ocaml/
in particular this link does not work anymore: https://ocaml-sf.org/learn-ocaml/howto-deploy-learn-ocaml-statically

I believe this is because the gh pages source has been set to ./ instead of ./docs,
so the HTML index unexpectedly comes from the README.md, instead of docs/index.md

@AltGr do you think this patch will work out-of-the-box as is, or I need to tweak another path?

If you're not sure, this can be tested after-the-fact anyway…

Checklist

• Read the CONTRIBUTING.md guide and:
  • Use Atomic Commits so each commit gathers a single logical change
  • Use Conventional Commits regarding commit messages (needed by our release toolchain)

Note to maintainers

• Read this wiki page.
• Make sure the PR has a milestone.
• Assign yourself before merging.
• Either do a regular merge:
  • for PRs containing several commits following conventional-commits,
  • or for PRs containing 1 commit shared with a later PR (to preserve the SHA1)
• Or do a squash-merge:
  • for PRs containing only 1 commit (not shared with a later PR),
  • or for PRs containing several commits that need not be kept in the history;
  • → Update the commit message header with a conventional-commit type,
  • → Add a footer Close #… if a related issue exists.

[AltGr]

Let's try it, there is no other way to check if it works anyway ^^

[AltGr]

Your fix worked 🎉
I also had to fix the OSX CI, but it had got broken by outside world changes.

[erikmd]

OK, thanks a lot @AltGr !