Fix a typo

Author: alexitkes

pandas/util/_decorators.py

@@ -239,7 +239,7 @@ def deprecate_nonkeyword_arguments(
 
     def decorate(func):
         if allowed_args is None:
-            spec = inspect.getfullargspec(func).args
+            spec = inspect.getfullargspec(func)
             allow_args = spec.args[: -len(spec.defaults)]
         else:
             allow_args = allowed_args