Fix error handler NoUpdate call

Author: T4rk1n

dash/_callback.py

@@ -507,7 +507,7 @@ def add_context(*args, **kwargs):
                             if not multi:
                                 output_value = NoUpdate()
                             else:
-                                output_value = [NoUpdate for _ in output_spec]
+                                output_value = [NoUpdate() for _ in output_spec]
                     else:
                         raise err