Fix CI status checks on PR from forks

[istandre]

Resolve #621

Description:

Pull requests coming from forks do not trigger the CI workflows. This is because the workflows only wait for a push and this cannot happen in this specific context.

This commit fixes the issue by also triggering workflows on pull_request events.

You can see that the workflows are waiting approval from a maintainer before starting: backend (3.9) action workflow

Checklist:

You should check all boxes before the PR is ready. If a box does not apply, check it to acknowledge it.

• ISSUE NUMBER. You linked the issue number (Ex: Resolve #XXX).
• PRE-COMMIT. You ran pre-commit on all commits, or else, you
  ran pre-commit run --all-files at the end.
• USER CHANGES. The changes are added to CHANGELOG.md and the documentation, if they impact
  our users.
• DEV CHANGES.
  • Update the documentation if this PR changes how to develop/launch on the app.
  • Update the README files and our wiki for any big design decisions, if relevant.
  • Add unit tests, docstrings, typing and comments for complex sections.

[istandre]

Note that if you would like to trigger the workflows regardless of approval status, the pull_request_target can also be added to the list. This will start the workflows, but in the base branch context. This to avoid abusive purposes, since the base branch is considered trusted.

[JosephMarinier]

Hello @istandre,

Thank you so much for looking into this! I have had a crazy week and I didn't find the time to look into #620 seriously. I am relieved that you found the issue. 😌

Thanks also for the very clear explanations. I didn't know any of this. 👍

Given the low volume of PRs on this repo, I think we'll be OK with approving the CI runs for now. I'll keep the pull_request_target option for the future.

Thanks again!