If this is an opern source repo on GitHub/GitLab, I think you could argue that the developer "made the data public" in giving it to you in the first place. That's an exception to the requirement to delete data. The same goes for public ledgers.
The tricky situation is when someone puts personal data not about themselves, but about a third party into a public ledger...
I've been reading through the text of the act, and while there is an exception allowing you to process data that has been made explicitly public by the person it relates to without asking them for permission, it seems to indicate that you still have to give them the ability to edit it later.
The tricky situation is when someone puts personal data not about themselves, but about a third party into a public ledger...