fix test

Author: KirillKurdyukov

src/Ydb.Sdk/src/Services/Topic/Reader/Reader.cs

@@ -206,6 +206,11 @@ await stream.Write(new MessageFromClient
 
     public ValueTask DisposeAsync()
     {
+        if (_disposeCts.IsCancellationRequested)
+        {
+            return ValueTask.CompletedTask;
+        }
+        
         _receivedMessagesChannel.Writer.TryComplete();
         _disposeCts.Cancel();
 

src/Ydb.Sdk/tests/Topic/ReaderIntegrationTests.cs

@@ -59,7 +59,7 @@ public async Task StressTest_WhenReadingThenCommiting_ReturnMessages()
             await message.CommitAsync();
         }
 
-        await reader.DisposeAsync();
+        await readerNext.DisposeAsync();
 
         await topicClient.DropTopic(new DropTopicSettings { Path = _topicName });
     }