I've noticed I'm in the same bucket as a few other users who've commented here — I've been added to the new Actions beta, but any repos I have that existed prior to that turnover are still attempting to use the older Action style. Is there something I can do to flip those older repos over?
It may be something uniquely weird to my account — I'm in an organization that also just added to the new beta, but it seems that the older repos in that organization made the transition fine.
I ran into this too. If you have previous workflow runs using the old actions beta, then you can go to github.com/<owner>/<repo>/actions and there's a button in the top right to upgrade the repo to the new version.
If you don't have previous workflow runs, it seems the only way to be able to upgrade is to run at least one workflow using the old system (a main.workflow file), then follow the steps above to upgrade to the new version. I've had to do this with every repo I wanna use the new actions beta with. It's a little annoying, but works.