This covers the GitHub Actions setup for automating Unity builds with GameCI and deploying them to itch.io with butler. Two workflow files do the work; everything is manually triggered.
The build and upload steps are separate so you can build without deploying, or re-deploy an old build without rebuilding. The upload workflow is reusable it can be called by the build workflow or triggered manually.
As next steps, I plan connecting this to GitHub Releases so that every push/merge to the main branch generates a draft of release notes (ie. with a release drafter) and a build artifact, and all I'd have to do afterwards is simply edit the release notes and hit a button.