This is quite an ambitious claim. Certainly the GitHub TOS grants them some common-sense ability to copy the code you upload so that they can usefully host it. Can you point to the portion that allows them to use it for Copilot?

Because I'm pretty sure it doesn't. Section D4:

> This license does not grant GitHub the right to sell Your Content. It also does not grant GitHub the right to otherwise distribute or use Your Content outside of our provision of the Service...