7 files declare their use of RequirementsInterface in Drupal 8

DestinationBase.php in core/modules/migrate/src/Plugin/migrate/destination/DestinationBase.php

FieldDiscovery.php in core/modules/migrate_drupal/src/FieldDiscovery.php

migrate_drupal.module in core/modules/migrate_drupal/migrate_drupal.module

Provides migration from other Drupal sites.

MigrationConfigurationTrait.php in core/modules/migrate_drupal/src/MigrationConfigurationTrait.php

MigrationPluginListTest.php in core/modules/migrate/tests/src/Kernel/Plugin/MigrationPluginListTest.php

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

Contains \Drupal\Tests\migrate\Unit\MigrationTest.

SqlBase.php in core/modules/migrate/src/Plugin/migrate/source/SqlBase.php