9 files declare their use of YamlDiscovery in Drupal 9

BreakpointManager.php in core/modules/breakpoint/src/BreakpointManager.php

ConfigMapperManager.php in core/modules/config_translation/src/ConfigMapperManager.php

ContextualLinkManager.php in core/lib/Drupal/Core/Menu/ContextualLinkManager.php

LinkRelationTypeManager.php in core/lib/Drupal/Core/Http/LinkRelationTypeManager.php

LocalActionManager.php in core/lib/Drupal/Core/Menu/LocalActionManager.php

LocalTaskIntegrationTestBase.php in core/tests/Drupal/Tests/Core/Menu/LocalTaskIntegrationTestBase.php

LocalTaskManager.php in core/lib/Drupal/Core/Menu/LocalTaskManager.php

MenuLinkManager.php in core/lib/Drupal/Core/Menu/MenuLinkManager.php

YamlDiscoveryTest.php in core/tests/Drupal/Tests/Core/Plugin/Discovery/YamlDiscoveryTest.php