Replace how outputs are set in GitHub Actions

[santisoler]

I noticed that magali is using the deprecated set-output command in GitHub Actions workflows. These should be updated to storing those variables in an environmental variable named GITHUB_OUTPUT.

For reference, here's the a blogpost for the deprecation: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

And a few PRs that apply the same change in our packages:

• Choclo: Update how output variables are stored in Actions choclo#90
• Boule: Update how output variables are stored in Actions boule#206
• Pooch: Update how output variables are stored in Actions pooch#425