fixed up typing bug that was showing up for Enum types

Author: tclose

pydra/utils/typing.py

@@ -549,7 +549,7 @@ def is_instance(
         candidates : type or ty.Iterable[type]
             the candidate types to check the object against
         """
-        if not isinstance(candidates, ty.Iterable):
+        if not isinstance(candidates, (tuple, list)):
             candidates = [candidates]
         for candidate in candidates:
             if candidate is ty.Any: