Only add x-dotnet-pub-seq-no when tracking enabled

If a user only enables publisher confirms for a channel, but _NOT_ automatic tracking, it will be up to them to correlate a `basic.return` with a sequence number.

Author: lukebakken

projects/RabbitMQ.Client/Impl/Channel.BasicPublish.cs

@@ -215,7 +215,7 @@ void MaybeAddActivityToHeaders(IDictionary<string, object?> headers,
 
             void MaybeAddPublishSequenceNumberToHeaders(IDictionary<string, object?> headers)
             {
-                if (_publisherConfirmationsEnabled)
+                if (_publisherConfirmationsEnabled && _publisherConfirmationTrackingEnabled)
                 {
                     byte[] publishSequenceNumberBytes = new byte[8];
                     NetworkOrderSerializer.WriteUInt64(ref publishSequenceNumberBytes.GetStart(), publishSequenceNumber);

projects/RabbitMQ.Client/Impl/Channel.PublisherConfirms.cs

@@ -228,7 +228,7 @@ private void HandleNack(ulong deliveryTag, bool multiple, bool isReturn)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private void HandleReturn(BasicReturnEventArgs basicReturnEvent)
         {
-            if (_publisherConfirmationsEnabled)
+            if (_publisherConfirmationsEnabled && _publisherConfirmationTrackingEnabled)
             {
                 ulong publishSequenceNumber = 0;
                 IReadOnlyBasicProperties props = basicReturnEvent.BasicProperties;