proposal: update node version to 20

[oliver139]

Checklist

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

Describe your proposal

According to the Github blog, actions using node 16 are deprecated. We should update this action to use node 20 asap.
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

Describe the solution you'd like

Updating specify file like .nvmrc and package.json from using node 16 to node 20. Certainly, a test is needed to see if node 20 is working fine on the action.

Describe alternatives you've considered

No response

Additional context

No response

[peaceiris]

Thanks.

[SukkaW]

@peaceiris Would you mind releasing a newer version under the v4 tag?