Add a warning for using snapshot() without match()?

[MarieLataretu]

After some time of confusion as to why the snapshot file was not generated, while the test passed, I discovered that I was missing the match() function:

        then {
                assert snapshot(workflow)
        }

This is especially unfavorable when you already have a snapshot file and think that everything is fine, since the test passed 🙈

I think, adding a warning for this usage would totally make sense, if it's possible.