proposal: Nightly or master version

[razonyang]

Checklist

• [X] I am using the latest version of this action.
• [X] I have read the latest README and followed the instructions.
• [X] I have read the latest GitHub Actions official documentation and learned the basic spec and concepts.

Describe your proposal

I would like to test my theme via using most latest version/commit that not release yet.

Describe the solution you'd like

Allow specify particular commit or branch as hugo-version, such as master.

Describe alternatives you've considered

No response

Additional context

No response