Creating a field storage in Kerneltests without the entity schema being installed is deprecated

In Kerneltests, creating a field storage on an entity in which the entity schema has not been installed is deprecated.

In Drupal 12.0.0, the deprecation warning will be replaced with a LogicException.

Example:

  // When the next line is missing the deprecation warning will be thrown.
  $this->installEntitySchema('entity_test');

  // Create a field storage on the entity "entity_test".
  Drupal\field\Entity\FieldStorageConfig::create([
    'field_name' => 'field_test',
    'entity_type' => 'entity_test',
    'type' => 'integer',
  ])->save();