Update FlowableOnBackpressureReduceTest.java

Author: akarnokd

src/test/java/io/reactivex/rxjava3/internal/operators/flowable/FlowableOnBackpressureReduceTest.java

@@ -115,7 +115,7 @@ public void reduceBackpressuredSync() {
         PublishProcessor<Integer> source = PublishProcessor.create();
         TestSubscriberEx<Integer> ts = new TestSubscriberEx<>(0L);
 
-        source.onBackpressureReduce((a, b) -> a + b).subscribe(ts);
+        source.onBackpressureReduce(Integer::sum).subscribe(ts);
 
         source.onNext(1);
         source.onNext(2);