core: Fix inFlightSubStreams counting on retry commit (#12649)

This PR fixes a race condition in RetriableStream where, under certain
retry and deadline timings, the response future may never be completed.

When a deadline cancellation occurs concurrently with retry commit,
inFlightSubStreams may not be decremented, causing
`ClientCallImpl.ClientStreamListenerImpl.closed` to never be invoked. As
a result, blockingUnaryCall can hang indefinitely.

After this change, the inFlightSubStreams counting is consistent
whenever a scheduled retry is committed, ensuring the close signal is
always delivered.

I verified this using the issue reproduction code from the issue
reporter, which previously caused blockingUnaryCall to hang and
eventually hit a TimeoutException because a while loop never progressed.
After this change, running the same reproduction code no longer hangs
and continues as expected without timing out.

Fixes #12620

Author: becomeStar

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

@@ -166,7 +166,8 @@ private Runnable commit(final Substream winningSubstream) {
 
       final boolean wasCancelled = (scheduledRetry != null) ? scheduledRetry.isCancelled() : false;
       final Future<?> retryFuture;
-      if (scheduledRetry != null) {
+      final boolean retryWasScheduled = scheduledRetry != null;
+      if (retryWasScheduled) {
         retryFuture = scheduledRetry.markCancelled();
         scheduledRetry = null;
       } else {
@@ -190,8 +191,10 @@ public void run() {
               substream.stream.cancel(CANCELLED_BECAUSE_COMMITTED);
             }
           }
-          if (retryFuture != null) {
-            retryFuture.cancel(false);
+          if (retryWasScheduled) {
+            if (retryFuture != null) {
+              retryFuture.cancel(false);
+            }
             if (!wasCancelled && inFlightSubStreams.decrementAndGet() == Integer.MIN_VALUE) {
               assert savedCloseMasterListenerReason != null;
               listenerSerializeExecutor.execute(