Feedback & fixes

[elijahr]

• Fix issue where unauthenticated hub could block CI waiting for user input
• Search for build-nim binaries via local text file cache, fall back to using hub only if auth credentials are present
• Fix issue on aarch64/arm64 where OS var hadn't been set yet
• Feedback from @smorimoto via https://github.com/asdf-vm/asdf-plugins/pull/343:
  • Test plugin against latest nim nightly
  • Pin plugin actions to v1