Fix RelatedUserWidget regressions from recent avatar changes.
Review Request #1688 — Created July 3, 2019 and updated
The `RelatedUserWidget` HTML includes information on user avatars for rendering purposes. Recently, Djblets avatar rendering was updated to provide HTML instead of just URLs for this widget, in order to support the fallback avatar service. This regressed some tests we had only on Review Board 4.0. This change updates the HTML comparison in a test for the new rendering. Testing Done: Unit tests pass against Django 1.6 and 1.11. Reviewed at https://reviews.reviewboard.org/r/10608/