fix: call ResponseMetadataHanlder#onTrailers before calling onClose

gax-grpc/src/main/java/com/google/api/gax/grpc/GrpcMetadataHandlerInterceptor.java

@@ -73,8 +73,8 @@ public void onHeaders(Metadata headers) {
 
               @Override
               public void onClose(Status status, Metadata trailers) {
-                super.onClose(status, trailers);
                 metadataHandler.onTrailers(trailers);
+                super.onClose(status, trailers);
               }
             };
         super.start(forwardingResponseListener, headers);