GitHub Actions doesn't have a lock file, so your repo is still prone to transitive attacks if the SHA-locked actions you use also happen to use other composite actions by tags, which could be compromised in the future.
Yes, it's maddening. Especially since it's a fair amount of effort to move to commit SHA pinning and establish a good maintenance/monitoring process around it; if I knew it would be adopted quickly, I could argue that people should just wait and accept temporary risk.
It would be cool if CI could inject a platform-wide lockfile into every remote download or lookup made by your scripts. So if you pull a container or git tag, the CI platform would automatically ensure that the exact digest downloaded is controlled by a lock file that you can inspect, check in, etc.