We changed the GitHub Actions self-hosted runner group default access to disable "Allow public repositories." This change impacts runner groups created before Sep 4, 2020 and changes those runner groups to a more secure default.
GitHub does not recommend the use of self-hosted runners with public repositories. If you are aware of the risks, and you choose to run workflows on your public repositories, you can update your runner group access to “Allow public repositories.”
Learn more about managing access to self-hosted runners.