You shouldn't have to though, they have a responsibility all their own to check that they have the rights regarding someone else's copyright before they do what they want to do, rather than to do it anyway and then to wait for the rights holder to come to them.

Copyright isn't 'opt in'.

I mean, if someone uploads a repo that contains proprietary code that also contains CI actions from the proprietary codebase, formatted the same as github actions, they're going to run those actions under the assumption that they are allowed to (even though they aren't, because it means they're running proprietary code). It's all automated. The person uploading the proprietary code would be the one infringing in that case.

Yes, but that's a different discussion. In this case the person does have the rights under the GPL to do what they do, but GitHub does not have an automatic right to assume that that gives them the right to enforce their ToS on the original copyright holder, which they effectively do.

> Copyright isn't 'opt in'.

Before 1989, copyright protection was opt-in in the US.

https://en.wikipedia.org/wiki/Copyright_notice

It's 2023.