6 files declare their use of VocabularyInterface in Zircon Profile 8

ForumUninstallValidator.php in core/modules/forum/src/ForumUninstallValidator.php

Contains \Drupal\forum\ForumUninstallValidator.

MigrateTaxonomyVocabularyTest.php in core/modules/taxonomy/src/Tests/Migrate/d7/MigrateTaxonomyVocabularyTest.php

Contains \Drupal\taxonomy\Tests\Migrate\d7\MigrateTaxonomyVocabularyTest.

OverviewTerms.php in core/modules/taxonomy/src/Form/OverviewTerms.php

Contains \Drupal\taxonomy\Form\OverviewTerms.

taxonomy.module in core/modules/taxonomy/taxonomy.module

Enables the organization of content into categories.

TaxonomyController.php in core/modules/taxonomy/src/Controller/TaxonomyController.php

Contains \Drupal\taxonomy\Controller\TaxonomyController.

Vocabulary.php in core/modules/taxonomy/src/Entity/Vocabulary.php

Contains \Drupal\taxonomy\Entity\Vocabulary.