Postgres fail in Drupal\Tests\path\Kernel\Migrate\d6\MigrateUrlAliasTest

Problem/Motivation

There's a 100% fail rate in Drupal\Tests\path\Kernel\Migrate\d6\MigrateUrlAliasTest for Postgres on 8.2.x and 8.3.x. See https://www.drupal.org/pift-ci-job/571613 for example.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes