The parent class is internal

Problem/Motivation

PHPUnit emits:

The "Symfony\Component\Cache\Adapter\AbstractTagAwareAdapter" class is considered internal. It may change without further notice. You should not use it from "Drupal\SymfonyCacheAdapter\DrupalPhpCacheAdapter"

This has been muted, see tests/fixtures/deprecation-ignore.txt.append

Proposed resolution

There's no direct replacement. To be investigated

Remaining tasks

User interface changes

API changes

Data model changes