6 files declare their use of FailureMarker

ApiController.php in core/modules/package_manager/tests/modules/package_manager_test_api/src/ApiController.php
FailureMarkerRequirementTest.php in core/modules/package_manager/tests/src/Functional/FailureMarkerRequirementTest.php
FailureMarkerTest.php in core/modules/package_manager/tests/src/Kernel/FailureMarkerTest.php
PackageManagerKernelTestBase.php in core/modules/package_manager/tests/src/Kernel/PackageManagerKernelTestBase.php
package_manager.install in core/modules/package_manager/package_manager.install
StageBaseTest.php in core/modules/package_manager/tests/src/Kernel/StageBaseTest.php

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