flutter_image uses run_test.sh to run a custom test environment instead of running normal unit tests. The tooling that ran those custom scripts was bespoke for flutter/packages, and unlike how all of our other tests now work, it only runs on changes to that package (rather than also always running in post-submit, and running for repo-wide changes like Flutter rolls).

When switching the tooling to a repo-tool based version, I found that it hangs on stable, and we just hadn't noticed yet because no PRs had touched that package since the last stable update. For now I'm excluding the test from stable to unblock the switch, but we should figure out why and re-enable it.