Update GitHub actions to use Ubuntu 22.04

[alessfg]

Proposed changes

Update GitHub actions to run on Ubuntu 22.04 and to only skip ~plus~ scenarios when the NGINX Plus license secrets are not present (it used to only run the scenarios during internal PRs).

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• [x] I have read the CONTRIBUTING document
• [x] I have added Molecule tests that prove my fix is effective or that my feature works
• [x] I have checked that any relevant Molecule tests pass after adding my changes
• [x] I have updated any relevant documentation (defaults/main/*.yml, README.md and CHANGELOG.md)