explicitly order results in get_helpful_votes_async

[escattone]

mozilla/sumo#1479

This PR fixes one of the primary causes of our flaky unit test runs. It turns out the root cause of the flakiness was because the HelpfulVote query in the get_helpful_votes_async view was not ordering the results, so it was left to the whims of Postgres to choose an ordering. So in the end, this turned out to be a MySQL vs. Postgres "gotcha". In MySQL prior to version 8, when using a GROUP BY clause without an explicit ORDER BY clause, an implicit ascending order is always used, which does not obey the SQL standard (i.e., no ordering should be applied). When I converted the query to Postgres a number of months ago, the results were no longer reliably ordered because Postgres does obey the standard, and so doesn't order the results. The solution is to add .order_by("date_created") to the HelpfulVote query.

[smithellis]

Awesome!