Basically it fires up elasticsearch using docker-compose and then the integration tests run against that. You could use a similar strategy to test different feature flag combinations.
For some of our private projects, we use kts to generate the github action yaml files using this: https://github.com/krzema12/github-workflows-kt
Well worth checking out if you have more complex workflows. Yaml is just horrible in terms of copy paste reuse. Also nice to get some compile time safety and auto complete with our action files.