Make rendered result (HTML files) downloadable

[das-g]

Issue description

Make the HTML files generated by the GitHub action downloadable. This would have several use-cases:

• check that workflows that do not trigger a deployment (for branches other than master) produced the expected result
• use the tutorial offline (see e.g. this question in our Gitter chatroom)

I guess this can be achieved by declaring result directory to be an artifact? (Here's GitHub's documentation on how to download GitHub Actions workflow artifacts.)

Language

all

Operating system

n/a

[ekohl]

check that workflows that do not trigger a deployment (for branches other than master) produced the expected result

I guess that makes sense can help with reviewing PRs. I would probably not generate them on pushes to master though since we already update gh-pages.

use the tutorial offline (see e.g. this question in our Gitter chatroom)

For that you can already download the gh-pages branch: https://github.com/DjangoGirls/tutorial/archive/refs/heads/gh-pages.zip