Aggregator tests should not rely on Classy
Problem/Motivation
Because of #3083275: [meta] Update tests that rely on Classy to not rely on it anymore and Classy being deprecated in Drupal 9 + removed in Drupal 10,: Tests that aren't specifically testing Classy yet declare $defaultTheme = 'classy'; should be refactored to use Stark as the default theme instead.
Proposed resolution
Change all tests in this module to use Stark as the default theme, and refactor the tests where needed so they continue to function properly.
Remaining tasks
User interface changes
API changes
Data model changes
Release notes snippet
Edited by drupalbot