Use node16 for GitHub Actions, instead of deprecated node12

[ChristianTellefsen]

Context

GitHub Actions log warnings about using deprecated node 12. This is the message:

Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: game-ci/unity-builder

Suggested solution

Update the actions to use node 16.

Additional details

[davidmfinol]

Fixed by #465