fix CI

Author: liufengyun

tests/pos-special/isInstanceOf/t2755.scala renamed to tests/neg-custom-args/isInstanceOf/t2755.scala

@@ -17,7 +17,7 @@ object Test {
     case x: Array[String]   => x.size
     case x: Array[AnyRef]   => 5
     case x: Array[_]        => 6
-    case _                  => 7
+    case _                  => 7   // error: only null is matched
   }
   def f3[T](a: Array[T]) = a match {
     case x: Array[Int]      => x(0)
@@ -26,7 +26,7 @@ object Test {
     case x: Array[String]   => x.size
     case x: Array[AnyRef]   => 5
     case x: Array[_]        => 6
-    case _                  => 7
+    case _                  => 7   // error: only null is matched
   }