Fix missing durration import

Author: Christoph Läubrich

platform-tests/src/test/java/org/junit/platform/reporting/open/xml/OpenTestReportGeneratingListenerTests.java

@@ -37,6 +37,7 @@
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.time.Duration;
 import java.util.Map;
 
 import org.junit.jupiter.api.AfterEach;