It is called LICENSE.txt. License your code as GPL and then Copilot can't reproduce bigger parts of your code.
But as long as you give the public access to your code, they can study it and learn from it. Humans and machines.
But as long as you give the public access to your code, they can study it and learn from it. Humans and machines.
If Copilot were to reproduce a larger part of, say, an MIT-licensed codebase or almost any other permissive licence, then they should legally provide attribution. I'm pretty sure that they don't even have an option to provide such specific attribution, which means that either they believe that the code copied from any one source is below the relevant threshold or they're just ignoring copyright.
It would be also the end of GitHub, as most users probably won’t accept such terms.