12 files declare their use of Item in Drupal 9

AggregatorItemViewsFieldAccessTest.php in core/modules/aggregator/tests/src/Kernel/Views/AggregatorItemViewsFieldAccessTest.php

AggregatorTitleTest.php in core/modules/aggregator/tests/src/Kernel/AggregatorTitleTest.php

DefaultProcessor.php in core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php

FeedParserTest.php in core/modules/aggregator/tests/src/Functional/FeedParserTest.php

FeedProcessorPluginTest.php in core/modules/aggregator/tests/src/Functional/FeedProcessorPluginTest.php

ItemCacheTagsTest.php in core/modules/aggregator/tests/src/Functional/ItemCacheTagsTest.php

ItemResourceTestBase.php in core/modules/aggregator/tests/src/Functional/Rest/ItemResourceTestBase.php

ItemTest.php in core/modules/jsonapi/tests/src/Functional/ItemTest.php

ItemWithoutFeedTest.php in core/modules/aggregator/tests/src/Kernel/ItemWithoutFeedTest.php

MigrateAggregatorItemTest.php in core/modules/aggregator/tests/src/Kernel/Migrate/d6/MigrateAggregatorItemTest.php

MigrateAggregatorItemTest.php in core/modules/aggregator/tests/src/Kernel/Migrate/d7/MigrateAggregatorItemTest.php

UpdateFeedItemTest.php in core/modules/aggregator/tests/src/Functional/UpdateFeedItemTest.php