Fastlane Flutter iOS TestFlight -- build flutter first

Fastfile

platform :ios do
  desc "Push a new beta build to TestFlight"
  lane :beta do
    # Build once with flutter to generate needed flutter files
    sh "cd ../.. && flutter build ios --release"
    
    # Now build the app as usual
    build_app(workspace: "Runner.xcworkspace", scheme: "Runner")
    
    upload_to_testflight
  end
  lane :bump do
    increment_build_number
  end
end