Warn users attempting to use Olivero as a base theme

andy-blum → closed merge request !2302

Tests failed because an exception that was not handled.

For the test failure.

Did not test.

The thrown exception is the following.

Exception: Warning: Undefined array key "user" olivero_preprocess_html()() (Line: 25)

Now the tests throw this exception.

Exception: Drupal\Component\Plugin\Exception\PluginNotFoundException: The "user_role" entity type does not exist.
Drupal\Core\Entity\EntityTypeManager->getDefinition()() (Line: 139)

It does not seem caused by the changes in this MR.

Reran the tests but they seem to be failing consistently.