This is literally the simplest possible thing, however… I wanted a workflow to be triggered only on successful execution of another workflow in GitHub Actions. I thought it will take somewhat more than the single workflow_run keyword!
It is one of the many triggeres available under the on: condition, and it will link one or many workflows to a secondary workflow. Beware, it does not act as a logical AND.
I put together a simple example on my account, here, I hope this helps. It helped me, given I wanted exactly that feature!