add test case

Author: liufengyun

tests/neg-custom-args/isInstanceOf/3324d.scala

@@ -0,0 +1,10 @@
+class Test {
+  val x: Any = ???
+
+  x match {
+    case _: List[Int @unchecked] => 5
+  }
+
+  def foo(x: Any): Boolean =
+    x.isInstanceOf[List[String]]  // error
+}