chore: auto compute prelease setting

Author: rickeylev

.github/workflows/release.yml

@@ -42,5 +42,6 @@ jobs:
           # Use GH feature to populate the changelog automatically
           generate_release_notes: true
           body_path: release_notes.txt
+          prerelease: ${contains(github.ref, "-rc")}
           fail_on_unmatched_files: true
           files: rules_python-*.tar.gz