Further work: Unit Test in go-cose repository needs to check for precise error condition

[yogeshbdeshpande]

This issue is an extension of already fixed issue #118

Issue #118 fixed the specific cases in verifier_test.go.

However after tidying up in file: verifier_test.go realized that a similar change is missing from other parts of go-cose unit test files.

This change covers the set for all go-cose files