fix mpu setup object size

Author: L-Applin

test/s3-tests/src/it/java/software/amazon/awssdk/services/s3/regression/DownloadStreamingRegressionTesting.java

@@ -235,7 +235,7 @@ static void doMultipartUpload(BucketType bucketType, String objectName, byte[] c
 
         List<CompletedPart> completedParts = new ArrayList<>();
         int partAmount = 10;
-        int partSize = 8 * 1024 * 1024;
+        int partSize = 6 * 1024 * 1024;
         for (int i = 0; i < partAmount; i++) {
             final int partNumber = i + 1;
             int startIndex = partSize * i;