8 files declare their use of ContextHandlerInterface in Drupal 9

BlockAccessControlHandler.php in core/modules/block/src/BlockAccessControlHandler.php

BlockComponentRenderArrayTest.php in core/modules/layout_builder/tests/src/Unit/BlockComponentRenderArrayTest.php

BlockRepository.php in core/modules/block/src/BlockRepository.php

FilteredPluginManagerTraitTest.php in core/tests/Drupal/Tests/Core/Plugin/FilteredPluginManagerTraitTest.php

SectionRenderTest.php in core/modules/layout_builder/tests/src/Unit/SectionRenderTest.php

SectionStorageManager.php in core/modules/layout_builder/src/SectionStorage/SectionStorageManager.php

SectionStorageManagerTest.php in core/modules/layout_builder/tests/src/Unit/SectionStorageManagerTest.php

SectionTest.php in core/modules/layout_builder/tests/src/Unit/SectionTest.php