This version makes no changes other than introducing PHP 8 language features so far, but all new features will be added to the 2.1.x branch from now on.
- Add the basic kernel test created in #3144399: Compatibility with Drupal 9.
- Add a missing @file doc comment.
- Ensure that the storage service resets its static cache when writing to the database.
- Add a menu link description for the admin UI.