Fixed #11929 -- Make sure YAML output order is helpful

[rixx]

By adopting Python 3.6+, this was already happening, but this test makes
sure we'll have no regression.

https://code.djangoproject.com/ticket/11929

[ngnpope]

I agree that ticket #11929 is resolved, but not purely by the fact that we are targeting Python 3.6+. I fixed this here by forcing PyYAML to treat dict as though it was an OrderedDict. This is because it used to force keys to be sorted. A "proper" fix would be to remove my workaround and add sort_keys=False here instead, but that would require enforcing pyyaml>=5.1.0 (which is probably not a bad thing given the security fix).

[rixx]

Thank you for your explanation. I can modify the PR to include your suggested changes, but I'm not clear on where/how to pin pyyaml to a minimum version, apart from the documentation. Do we have other places where we check for optdepdend versions?

[ngnpope]

I wouldn't make the change at this stage unless the the community agrees to pin the version. So for now just take my comment as being the correct explanation as to why this is resolved.

[rixx]

I'll add it to the commit message, for correctness' sake 😉

[felixxm]

I checked and this has been originally fixed in 5bc3123.

[felixxm]

This is already tested in SerializersTestBase.test_deterministic_mapping_ordering().