My interpretation of the GitHub TOS section D4 would give give GitHub the right to parse your code and/or make incedental copies regardless of what your license states.

https://docs.github.com/en/github/site-policy/github-terms-o...

This is the same reason it doesn’t matter if you put up a license that forbids GitHub from including you in backups or the search index.

Then the person training the models wouldn't be legally accessing your code.