[Fastlane.Swift] When FastlaneRunner fails, the exit code is 0 instead of 1

[pchmelar]

New Issue Checklist

• Updated fastlane to the latest version
• I read the Contribution Guidelines
• I read docs.fastlane.tools
• I searched for existing GitHub issues

Issue Description

When swift run fastlaneRunner lane [lane] fails with some error, the exit code is 0. This presents a serious issue when running on CI, as the job fails, but a pipeline doesn't stop. The solution would be to handle this in onError, but that's not possible when using Fastlane.swift via SPM. 😥 It is already resolved in this PR - #20563 - can we please merge it? 🙏 It's the only major issue preventing us from using Fastlane.swift in production.

[pchmelar]

@rogerluan @lacostej 🙏 🙏