10 files declare their use of RequirementsPageTrait in Drupal 9

InstallerTestBase.php in core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php

InvalidUpdateHookTest.php in core/modules/system/tests/src/Functional/UpdateSystem/InvalidUpdateHookTest.php

LocaleTranslatedSchemaDefinitionTest.php in core/modules/locale/tests/src/Functional/LocaleTranslatedSchemaDefinitionTest.php

MinimalTest.php in core/profiles/minimal/tests/src/Functional/MinimalTest.php

NoPreExistingSchemaUpdateTest.php in core/modules/system/tests/src/Functional/UpdateSystem/NoPreExistingSchemaUpdateTest.php

StandardTest.php in core/profiles/standard/tests/src/Functional/StandardTest.php

UpdateCacheTest.php in core/modules/system/tests/src/Functional/UpdateSystem/UpdateCacheTest.php

UpdateSchemaTest.php in core/modules/system/tests/src/Functional/UpdateSystem/UpdateSchemaTest.php

UpdateScriptTest.php in core/modules/system/tests/src/Functional/UpdateSystem/UpdateScriptTest.php

UpdatesWith7xTest.php in core/modules/system/tests/src/Functional/UpdateSystem/UpdatesWith7xTest.php