It seems like they could just download your code from Github and violate your license like that so.. unclear why they'd bother doing it via copilot.
Why would specifically prompting the LLM to generate similarly copyrighted code be any different? That's what's being discussed here - that people will "go the extra lengths" to intentionally copy your code.
The "It wasn't me, it was the tool, even though I directed the tool quite specifically to do the thing that happened" is not a new defense in the legal systems of the world. We are already generally are able to deal with these without significant issue.
If it were my GPLed code being copied, it doesn't seem to make any difference whether I press copyright claims or not. It won't help me compete against this dev's company. They'd use Copilot to rewrite the code differently. The speed of improvement in code-writing tools doesn't give me much hope that my code is uniquely clever.