No, the license that you apply is completely irrelevant, and there’s certainly nothing whatsoever special about the GPL. Copilot is completely depending on being effectively exempt from copyright; if that legal theory falls apart, the entire space (and a lot of other machine learning stuff) is utterly doomed. Trouble is, Copilot can’t tell whether it’s reproducing copyrightable chunks of your code, or indeed where what it produces came from, by the very nature of machine learning techniques.