Only run unit tests after explicit approval

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Currently, we use a custom environment named testing to only run our unit tests when approved. This is to avoid unnecessary strain on GitHub servers when a commit is pushed to a PR as many commits might not require extra unit tests to run and a few commits at the end of a PR with unit tests run should suffice.

However, with this approach the commit view in PRs clutters as described in my comment here. See that thread for more background information. Unfortunately, there's probably not much we can do for right now, except for waiting that the GitHub team might pick up our request.

References

• https://github.com/orgs/community/discussions/25100
• https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#issue_comment-on-issues-only-or-pull-requests-only
• https://docs.github.com/de/webhooks/webhook-events-and-payloads#issues
• https://stackoverflow.com/a/59349906/
• This might be another possible way to achieve it via comment triggers in a PR: https://stackoverflow.com/a/75087724/