[meta] Fix failing tests for various moved-to-contrib modules to ensure a reliable upgrade path for D9 sites

Problem/Motivation

Numerous of the moved-to-contrib modules have failing test suites due to changes in core close to the beta deadline such as other removed modules and themes.

List of test suites that are currently failing:

• Aggregator
• RDF

Proposed resolution

Fix these test failures so that we can ensure the modules continue to work with Drupal 9.5 and 10 so that sites' upgrades to D10 are reliable and smooth.

Remaining tasks

• #3294389: Fix fails in HEAD (Aggregator)
• #3313046: Refactor RDF tests to use core Drupal 10 themes
• #3313047: HAL tests require RDF

Add child issues as necessary.

Release notes snippet