Merge pull request #6234 from dotty-staging/fix/i5338

Fix #5338: test previously non-compiling code

Author: nicolasstucki

tests/pos/i5338.scala

@@ -0,0 +1,6 @@
+object Test {
+  val unit = ()
+
+  def f[T <: Tuple, X](xs: T, x: X) =
+    xs ++ x *: unit
+}