6 files declare their use of MigrateImportEvent in Drupal 10

MigrateEventsTest.php in core/modules/migrate/tests/src/Kernel/MigrateEventsTest.php

MigrateExecutable.php in core/modules/migrate/src/MigrateExecutable.php

MigrateImportEventTest.php in core/modules/migrate/tests/src/Unit/Event/MigrateImportEventTest.php

MigrateUpgradeImportBatch.php in core/modules/migrate_drupal_ui/src/Batch/MigrateUpgradeImportBatch.php

NodeTranslationMigrateSubscriber.php in core/modules/node/src/EventSubscriber/NodeTranslationMigrateSubscriber.php

PluginEventSubscriber.php in core/modules/migrate/src/Plugin/PluginEventSubscriber.php