https://docs.github.com/en/site-policy/github-terms/github-t...
(The link I posted is also not the proper ToS, it is more of an abridged version. They made the actual ToS somewhat hard to find and I cannot be bothered.)
> Short version: We treat the content of private repositories as confidential, and we only access it as described in our Privacy Statement—for security purposes, to assist the repository owner with a support matter, to maintain the integrity of the Service, to comply with our legal obligations, if we have reason to believe the contents are in violation of the law, or with your consent.
> You grant us and our legal successors the right to store, archive, parse, and display Your Content, and make incidental copies, as necessary to provide the Service, including improving the Service over time.
> parse it into a search index or otherwise analyze it on our servers
This is an “AI” platform now. “Improving the service” means that. “With your consent” means you have accepted the ToS (which by the way can be changed at any point and your continued use of the service means you consent to it).