fix scala#9482: add pos test

Author: bishabosha

tests/pos/i9482.scala

@@ -0,0 +1,11 @@
+import scala.reflect.OptManifest
+
+object Ref {
+  def make[A: OptManifest]: Ref[A] = ???
+}
+trait Ref[A]
+
+trait Foo[A] {
+  val bar = Ref.make[Int]
+  val baz: Ref[A] = Ref.make
+}