Add Github Actions CI/CD

[vexx32]

PR Summary

Azure Pipelines seems determined to make things difficult, so I'm gonna try out moving things over to Github Actions here.

Changes

• [x] Added github.yml
• [x] Update files to set GHA environment variables correctly.

Checklist

• [X] Pull Request has a meaningful title.
• [X] Summarised changes.
• [ ] Pull Request is ready to merge & is not WIP.
• [ ] Added tests / only testable interactively.
  • Make sure you add a new test if old tests do not effectively test the code changed.
• [ ] Added documentation / opened issue to track adding documentation at a later date.