How do you test workflow_run actions?

Since workflow_run triggered actions only run the code in the default branch, how do you develop and test that they are working before merging a PR? I’m attempting to build our CI/CD pipeline, and I would like to trigger a workflow_run action to run on our default branch after the CI runs on it to deploy to our QA environment, but I see no way of testing that everything is working without merging the action.