Scheduled workflows run on the latest commit on the default branch.
Note: The default branch is also the initial branch that Git checks out locally when someone clones the repository. Unless you specify a different branch, the default branch in a repository is the base branch for new pull requests and code commits.
Reference:
https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax
https://docs.github.com/articles/about-branches