Update tests/run/tuple-concat.scala

Check that concatenation with an empty tuple returns the original reference

Co-Authored-By: Nicolas Stucki <nicolas.stucki@gmail.com>

Author: brunnerant

tests/run/tuple-concat.scala

@@ -10,4 +10,6 @@ object Test extends App {
   println("tuple2 ++ emptyTuple = " + (tuple2 ++ emptyTuple))
   println("emptyTuple ++ tuple2 = " + (emptyTuple ++ tuple2))
   println("tuple1 ++ tuple2 = " + (tuple1 ++ tuple2))
+  assert((tuple1 ++ emptyTuple) eq tuple1)
+  assert((emptyTuple ++tuple1) eq tuple1)
 }