You are trying to run a build with a Flutter Test Step included but it is stuck with this message:
"Waiting for another flutter command to release the startup lock..."
The issue happens if your test requires a dependency that isn't brought in correctly. In these cases, Flutter freezes with the startup lock error. This is what the error suggests.
Unfortunately, this is an issue with Flutter itself, and what you can do is try to narrow down which test is causing the problem.
Try to clear your cache and remove any caching Step from you Workflow. If this fixes the issue, then that would mean that Flutter was trying to pull in a bad cached dependency.