AFAIK that's irrelevant per GitHub's TOS, which users agree to:
By setting your repositories to be viewed publicly, you agree to allow others to view and "fork" your repositories (this means that others may make their own copies of Content from your repositories in repositories they control).
If you set your pages and repositories to be viewed publicly, you grant each User of GitHub a nonexclusive, worldwide license to use, display, and perform Your Content through the GitHub Service and to reproduce Your Content solely on GitHub as permitted through GitHub's functionality (for example, through forking).
AIUI you therefore always have the right to fork something on GitHub.
https://docs.github.com/en/site-policy/github-terms/github-t...