[go_router_builder] Fixes an deprecated warning for using withNullability#9158

auto-submit[bot] merged 3 commits intoflutter:mainflutter/packages:mainfrom

raju-muliyashiya:remove-withNullability-deprecate-warningraju-muliyashiya/flutter_packages:remove-withNullability-deprecate-warningCopy head branch name to clipboard