Change error message of a failing `assert_eq!`

tcsc:

If ~1/3 of the uses choose one order, and the other ~2/3 use the other order, I don't think that's enough of a consensus for us to codify.

Those proportions are not indicative of consensus, they are indicative of ambiguity. An ambiguity which hurts understanding of test output.

As to which should be picked, I wouldn't be upset if someone flipped a coin. Non-ambiguous would be better than the status quo. That said obviously it should be (actual, expected) as it is alphabetic.