9 files declare their use of KeyValueStoreInterface in Drupal 9

EntityAutocompleteController.php in core/modules/system/src/Controller/EntityAutocompleteController.php

EntityFieldManagerTest.php in core/tests/Drupal/Tests/Core/Entity/EntityFieldManagerTest.php

Contains \Drupal\Tests\Core\Entity\EntityFieldManagerTest.

FieldDefinitionListenerTest.php in core/tests/Drupal/Tests/Core/Field/FieldDefinitionListenerTest.php

KeyValueEntityStorage.php in core/lib/Drupal/Core/Entity/KeyValueStore/KeyValueEntityStorage.php

MigrateSourceTest.php in core/modules/migrate/tests/src/Unit/MigrateSourceTest.php

Contains \Drupal\Tests\migrate\Unit\MigrateSourceTest.

UpdateHookRegistry.php in core/lib/Drupal/Core/Update/UpdateHookRegistry.php

UpdateHookRegistryTest.php in core/tests/Drupal/Tests/Core/Update/UpdateHookRegistryTest.php

UpdateRegistry.php in core/lib/Drupal/Core/Update/UpdateRegistry.php

UpdateRegistryTest.php in core/tests/Drupal/Tests/Core/Update/UpdateRegistryTest.php