GitHub’s EULA gives GitHub permission to train Copilot on public code you host on GitHub regardless of the license you have chosen for that code.

Even without this, in terms of copyright, since Copilot doesn’t do what your public code does, and it only uses your code to train, it is a transformative use, and would be fair use. It’s possible that a court case will find otherwise, but I think that’s unlikely. The only case I think it will become disallowed, is if Congress passes a law about it.

If Congress does pass such a law, GitHub’s market power in this domain only goes up, since the EULA gives it the covenants.