These AI systems are all riding on fair use anyway (at least for now), so it doesn't matter what license you choose because they're never accepting it in the first place.
My understanding is that Microsoft makes an effort to exclude all GPL software from its training. (Is this true?)
What we need is a more permissive MIT- or BSD-style license that defeats Copilot.
We just need to convince law-abiding companies that they must not use the code.