On 401 for fetching GitHub Repos then retry without auth for public repos and emit error about incorrect GH Auth token

[kentbull]

When collectExternalReferences() is run with an invalid GITHUB_API_TOKEN, public GitHub Pages content still loads successfully, but the GitHub API branch lookup fails with 401, producing misleading errors like “Could not get commit hash from main branch”.

Expected:

• If the repo is public, retry the branch lookup without auth after a 401, or
• downgrade this to a warning that the token is invalid/stale, since term collection can still succeed.

Also, the warning text references GITHUB_PAT, while the code reads GITHUB_API_TOKEN.