Backport PR #13187: Fix wrong inspect.signature call

IPython/core/completer.py

@@ -1496,7 +1496,7 b' class IPCompleter(Completer):'
                   inspect.Parameter.POSITIONAL_OR_KEYWORD)
 
         try:
-            sig = inspect.signature(call_obj)
+            sig = inspect.signature(obj)
             ret.extend(k for k, v in sig.parameters.items() if
                        v.kind in _keeps)
         except ValueError: