Outside collaborators can't be added to GitHub teams, team membership is
restricted to org members.

https://docs.github.com/en/organizations/managing-user-access-to-your-organizations-repositories/managing-outside-collaborators/adding-outside-collaborators-to-repositories-in-your-organization#:~:text=Outside%20collaborators%20cannot%20be%20added%20to%20a%20team%2C%20team%20membership%20is%20restricted%20to%20members%20of%20the%20organization

Release Notes:

- N/A