Same as what you have to use in gitlab, for what that's worth. But it is interesting that their existing "main.workflow" file is in a different syntax.
Ahh, now I see, support for the main.workflow syntax will be removed, and you must migrate:
That’s disappointing. The original Actions was amazing and much of that was the thoughtful main.workflow file. This feels like a regression. I’m not a yaml hater like many but main.workflow was clean, almost pleasant to use. It felt like it actually came from understanding developers.
Ahh, now I see, support for the main.workflow syntax will be removed, and you must migrate:
https://help.github.com/en/articles/migrating-github-actions...