fix for METH_O invocation, don't wrap the single argument in a tuple

Author: timfel

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/TruffleCextBuiltins.java

@@ -1576,7 +1576,7 @@ public Object execute(VirtualFrame frame) {
             Object arg = readArgNode.execute(frame);
             Object[] arguments = PArguments.create(2);
             PArguments.setArgument(arguments, 0, self);
-            PArguments.setArgument(arguments, 1, factory.createTuple(new Object[]{arg}));
+            PArguments.setArgument(arguments, 1, arg);
             return directCallNode.call(arguments);
         }
     }