Fix Sts flakey test (#6979)

Author: davidh44

services/sts/src/test/java/software/amazon/awssdk/services/sts/internal/StsRetryStrategyTest.java

@@ -18,7 +18,6 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.mock;
 
-import java.time.Duration;
 import java.util.stream.Stream;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -98,7 +97,8 @@ void assertRetriesOnIdpCommunicationException(RetryStrategy strategy) {
                                                                    .token(token)
                                                                    .failure(failure)
                                                                    .build();
-        assertThat(strategy.refreshRetryToken(refresh).delay()).isGreaterThan(Duration.ZERO);
+        // Should not throw TokenAcquisitionFailedException
+        assertThat(strategy.refreshRetryToken(refresh)).isNotNull();
     }
 
     private static Stream<Arguments> retryModeResolutionCases() {