Change delay for hedging retry after a non-fatal error to be 0 to match the gRFC A6. (#10293)

Fixes #10145

Author: larry-safran

core/src/main/java/io/grpc/internal/RetriableStream.java

@@ -1067,6 +1067,10 @@ private HedgingPlan makeHedgingDecision(Status status, Metadata trailer) {
           isThrottled = !throttle.onQualifiedFailureThenCheckIsAboveThreshold();
         }
       }
+      if (!isFatal && !isThrottled && !status.isOk()
+          && (pushbackMillis != null && pushbackMillis > 0)) {
+        pushbackMillis = 0; // We want the retry after a nonfatal error to be immediate
+      }
       return new HedgingPlan(!isFatal && !isThrottled, pushbackMillis);
     }
 

core/src/test/java/io/grpc/internal/RetriableStreamTest.java

@@ -2518,7 +2518,7 @@ public void hedging_pushback_positive() {
         Status.fromCode(NON_FATAL_STATUS_CODE_1), PROCESSED, headers);
 
     fakeClock.forwardTime(HEDGING_DELAY_IN_SECONDS, TimeUnit.SECONDS);
-    inOrder.verifyNoMoreInteractions();
+    inOrder.verify(retriableStreamRecorder).newSubstream(anyInt());
 
     fakeClock.forwardTime(1, TimeUnit.SECONDS);
     assertEquals(1, fakeClock.numPendingTasks());