Debug: Restore website deployment to GitHub Pages

[NPDebs]

This PR fixes #994 - thanks again for flagging, Yo!

In #948, a new GitHub Action was added, which primarily provides a live deploy preview link under each open Pull Request.
However, the previous Action that handled deployment to GitHub pages was removed in the process. This PR addresses the resulting effects of that...action. :-)

👍🎉 First of all, thanks for taking the time to contribute! 🎉👍

FOR CONTRIBUTOR

• I have read the CONTRIBUTING.md document

PR Type:

• This PR adds a new blog post
• This PR does something else (explain above)

FOR REVIEWERS

Thanks for taking the time to review! ❤️

Here are the list of things to make sure of:

• The website builds (a check will fail if not)
• All images have been added within the Pull Request and they have Alt text
• If there are paragraphs or text, the key messages are highlighted
• All internal links (within OLS website) use the {% link path_to_file.md %} format
• The preview corresponds to the changes described in the Pull Request
• The code is tidy and passes the linting tests

[NPDebs]

Making these changes from a branch in my fork was not a very bright idea, because of the organisation-level access tokens (which I clearly do not have 😅) required to run these jobs.

[NPDebs]

✍️ For the same reason, only PRs from branches created in the main website repo will generate a deploy preview. (see #996, #998)

Branches not created directly in the open-life-science.github.io repo (those created on forks) will not deploy or generate preview, for lack of access to environmental variables. (see #995, #997)

Compare #995 & #996; #997 & #998.

Action: Find a way to workaround permission issues.