Unless I am missing something, it seems that you only need to use something like the following that was (obtained using quick search, haven't tried)

https://archclx.medium.com/enforcing-gpg-encryption-in-githu...

My opinion on the matter is that AI models stealing the open source code would be ok IF the models are also open and remain so, and the services like chatgpt will remain free of cost (at least a free tier), and remain free of ads.

But we all know how it is going to go.