8 files declare their use of ServiceProviderInterface in Zircon Profile 8

CoreServiceProvider.php in core/lib/Drupal/Core/CoreServiceProvider.php

Contains \Drupal\Core\CoreServiceProvider.

DrupalKernel.php in core/lib/Drupal/Core/DrupalKernel.php

Contains \Drupal\Core\DrupalKernel.

InstallerServiceProvider.php in core/lib/Drupal/Core/Installer/InstallerServiceProvider.php

Contains \Drupal\Core\Installer\InstallerServiceProvider.

KernelTestBase.php in core/tests/Drupal/KernelTests/KernelTestBase.php

Contains \Drupal\KernelTests\KernelTestBase.

RouterTestServiceProvider.php in core/modules/system/tests/modules/router_test_directory/src/RouterTestServiceProvider.php

Contains \Drupal\router_test\RouterTestServiceProvider.

SerializationServiceProvider.php in core/modules/serialization/src/SerializationServiceProvider.php

Contains \Drupal\serialization\SerializationServiceProvider.

TestServiceProvider.php in core/modules/simpletest/src/TestServiceProvider.php

Contains \Drupal\simpletest\TestServiceProvider.

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

Contains \Drupal\Core\Update\UpdateServiceProvider.