9 files declare their use of DiagnosticCheckInterface in Purge 8.3

AlwaysErrorDiagnosticCheck.php in tests/modules/purge_check_error_test/src/Plugin/Purge/DiagnosticCheck/AlwaysErrorDiagnosticCheck.php

AlwaysInfoDiagnosticCheck.php in tests/modules/purge_check_test/src/Plugin/Purge/DiagnosticCheck/AlwaysInfoDiagnosticCheck.php

AlwaysOkDiagnosticCheck.php in tests/modules/purge_check_test/src/Plugin/Purge/DiagnosticCheck/AlwaysOkDiagnosticCheck.php

AlwaysWarningDiagnosticCheck.php in tests/modules/purge_check_warning_test/src/Plugin/Purge/DiagnosticCheck/AlwaysWarningDiagnosticCheck.php

DiagnosticsCommand.php in modules/purge_drush/src/Commands/DiagnosticsCommand.php

PurgerSpecificWarningDiagnosticCheck.php in tests/modules/purge_check_test/src/Plugin/Purge/DiagnosticCheck/PurgerSpecificWarningDiagnosticCheck.php

QueueSpecificWarningDiagnosticCheck.php in tests/modules/purge_check_test/src/Plugin/Purge/DiagnosticCheck/QueueSpecificWarningDiagnosticCheck.php

ServiceSmokeAndFireTest.php in tests/src/Kernel/DiagnosticCheck/ServiceSmokeAndFireTest.php

ServiceTest.php in tests/src/Kernel/DiagnosticCheck/ServiceTest.php