Update to use partial instead of lambda function

Author: markusdap

graphene/core/classtypes/uniontype.py

@@ -1,3 +1,5 @@
+from functools import partial
+
 import six
 from graphql.core.type import GraphQLUnionType
 
@@ -35,6 +37,6 @@ def internal_type(cls, schema):
         return GraphQLUnionType(
             cls._meta.type_name,
             types=list(map(schema.T, cls._meta.types)),
-            resolve_type=lambda instance, info: cls._resolve_type(schema, instance, info),
+            resolve_type=partial(cls._resolve_type, schema),
             description=cls._meta.description,
         )