The fundamental problem is that on Github Actions it's possible to give read-only permissions to pipelines that are then violated because runners can be granted read+write permissions to the cache. And they don't consider this a P0 bug.

So you don't even need to see questionable bash scripts to know there's a problem. The script would have already completed and pwned you by the time you see it.

With podman or nix you would have to poison the container registry/nix store which is more difficult, but you're also probably using your own runners.

My point though is that it's not bash or yaml here, but Github's default access controls. If you own your own runners and your own caching layer then you're not going to be nearly as boneheaded as Github here. But Github pushes people towards their integrated solutions, which have horrible defaults.