End-to-end JSON API test sporadically fails

[Atul Varma]

The test_end_to_end[JSONParser-JSONRenderer] sporadically fails with an unintelligible diff.

I've noticed this locally and on a number of CI builds lately, likely introduced by #936.

Here's an example.

I suspect it might be happening because the JSON is just being serialized with a different key ordering or something, but it's just a guess.