Earlier quoted context omitted.
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.
I'd love to see ML-GPL which specifically deals with using licensed property as a training set.
Or specifically no closed-source or closed-data tools. I wouldn't mind if a non-profit org wanted to help, but it's Microsoft—and they want to sell it back to us in the future.