Fix handling of UpdateBehavior.WRITE_IF_NOT_EXISTS on @DynamoDbAutoGeneratedUuid

Author: anasatirbasa

services-custom/dynamodb-enhanced/src/test/java/software/amazon/awssdk/enhanced/dynamodb/extensions/AutoGeneratedUuidExtensionTest.java

@@ -89,9 +89,7 @@ public void beforeWrite_withExistingUuid_doesNotOverwriteValue() {
 
         String uuidValue = result.transformedItem().get("uuidAttribute").s();
         isValidUuid(uuidValue);
-        assertThat(uuidValue)
-            .as("UUID must be preserved, not overwritten")
-            .isEqualTo(initialUuid);
+        assertThat(uuidValue).isEqualTo(initialUuid);
     }
 
     @Test
@@ -135,8 +133,8 @@ public void beforeWrite_withEmptyUuid_generatesNewValue() {
                                            .build());
 
         assertThat(result.updateExpression()).isNull();
-        String out = result.transformedItem().get("uuidAttribute").s();
-        isValidUuid(out);
+        String uuidValue = result.transformedItem().get("uuidAttribute").s();
+        isValidUuid(uuidValue);
     }
 
     @Test