CI: Improve GitHub actions

[htdat]

After this is solved #634, we can consider these improvements for GitHub actions:

• Code Coverage
• Auto deploy to WP.org for new tags
• Upgrade npm and composer packages
• Consider using artifact https://docs.github.com/en/actions/guides/storing-workflow-data-as-artifacts
• Cache for GitHub Actions https://docs.github.com/en/actions/guides/caching-dependencies-to-speed-up-workflows