${{}} is the notation for a string replacement.
You can see from the string that the token is being retrieved from your GitHub repository secrets. It doesn't matter if the repository itself is public or private, secrets are secret.
See this link for more information about secrets: https://docs.github.com/en/actions/security-guides/encrypted-secrets
The yml file itself is public, so always ensure that sensitive information about your project/organisation or credentials are stored as secrets in GitHub rather than strings in the yml file.