ghasum verify should error for redundant checksums

[ericcornelissen]

Summary

By default the ghasum verify command should complain about stored checksums that aren't used. This should help keep the sumfile up-to-date with the repository. The main motivation for this is to ensure that the sumfile always changes when the set of Actions used by a project changes.

Notes

• In relation to Support validating a specific workflow #1 and Support validating a specific job #2, this behavior should only apply when a whole repository is being verified. In the case of partial verification it is expected that some checksums are redundant.