chore: update Node.js to v24 which is active LTS

[exoego]

Fixes #83

Thanks for this action.

I've noticed this action uses node20, which will be removed 2026-09-16.
This PR bumps node to 24.

[Vampire]

Thanks for your contribution.
Please don't wonder if I don't merge it right now.
It has some issues though.

• this is a breaking change so misses a first commit that increases the major version
• no conventional commit messages here
• you don't refer to the issue you fix in the commit message

You can see in the history of the repo how to do it properly.

But anyway I'd like to have a go on #76 and #82 first which should also make tests green. But for that I don't have the time right now. That would maybe also fix the first point in the list.