Make TypeBuiltins$MroAttrNode subclass of PythonUnaryBuiltinNode

Author: steve-s

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/type/TypeBuiltins.java

@@ -303,7 +303,7 @@ static Object doc(Object self, @SuppressWarnings("unused") DescriptorDeleteMarke
 
     @Builtin(name = J___MRO__, minNumOfPositionalArgs = 1, isGetter = true)
     @GenerateNodeFactory
-    abstract static class MroAttrNode extends PythonBuiltinNode {
+    abstract static class MroAttrNode extends PythonUnaryBuiltinNode {
         @Specialization
         static Object doit(Object klass,
                         @Bind("this") Node inliningTarget,