fix(ci): improve attribution of co-authors

[zvolin]

Description

Fix the Co-authored-by inclusion in commit messages so that co-authorship is properly expressed. Additionally, filter merge commits before unique authors. Previously, we would not attribute an author if their first commit in a PR was a merge commit. Finally, we remove superfluous newlines between the Co-authored-by lines.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

Thank you and sorry again that this didn't work properly.

As mentioned in the other PR I am in contact with GitHub support about this.

[zvolin]

I'm also wondering if it will work with an empty lines between multiple co-authored-by, here github docs mentions it should on the very end, and we got something like this
85a846a

[thomaseizinger]

I'm also wondering if it will work with an empty lines between multiple co-authored-by, here github docs mentions it should on the very end, and we got something like this
85a846a

I was bothered with the empty lines too, although so far I considered it to be purely cosmetic.

I did open a discussion upstream already but hadn't had the time yet to try it out: Mergifyio/mergify#5091

I used https://j2live.ttl255.com/ in the past to test out the template rendering without having to iterate by merging PRs. The commits data structure is documented here: https://docs.mergify.com/configuration/#commits

[thomaseizinger]

Argh, I forgot that mergify doesn't support updating variables within a loop.

[thomaseizinger]

Yey! I think I managed to get this to work!