Forgejo Runner v13.0.0 is available

Forgejo Runner v13.0.0 introduces several breaking changes focused on security and predictability. Three insecure workflow commands — add-path, set-env, and set-output — have been removed and replaced with environment file-based alternatives (FORGEJO_PATH, FORGEJO_ENV, FORGEJO_OUTPUT). Docker credential handling has been tightened to prevent credentials from being sent to unexpected registries. Invalid workflow syntax and expression interpolation errors now fail jobs instead of logging warnings. The minimum Docker version requirement has been raised to 25.0, with a known IPv6 bug fixed in Docker v28.0.1. Several legacy GITEA_* environment variables and the container.network_mode config option have also been removed.