7 files declare their use of Tasks in Drupal 9

Tasks.php in core/tests/fixtures/database_drivers/custom/fake/Install/Tasks.php

Tasks.php in core/tests/fixtures/database_drivers/core/corefake/Install/Tasks.php

Tasks.php in core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php

Tasks.php in core/lib/Drupal/Core/Database/Driver/pgsql/Install/Tasks.php

Tasks.php in core/lib/Drupal/Core/Database/Driver/mysql/Install/Tasks.php

Tasks.php in core/tests/fixtures/database_drivers/module/corefake/src/Driver/Database/corefake/Install/Tasks.php

Tasks.php in core/tests/fixtures/database_drivers/module/corefake/src/Driver/Database/corefakeWithAllCustomClasses/Install/Tasks.php