Minor alignment with upstream

Replicates graphql/graphql-js@126b572
and graphql/graphql-js@ded3859

Author: Cito

graphql/utilities/extend_schema.py

@@ -198,15 +198,14 @@ def extend_input_object_type(
         )
 
     def extend_input_field_map(type_: GraphQLInputObjectType) -> GraphQLInputFieldMap:
-        old_field_map = type_.fields
         new_field_map = {
             field_name: GraphQLInputField(
                 cast(GraphQLInputType, extend_type(field.type)),
                 description=field.description,
                 default_value=field.default_value,
                 ast_node=field.ast_node,
             )
-            for field_name, field in old_field_map.items()
+            for field_name, field in type_.fields.items()
         }
 
         # If there are any extensions to the fields, apply those here.
@@ -397,7 +396,6 @@ def extend_implemented_interfaces(
     def extend_field_map(
         type_: Union[GraphQLObjectType, GraphQLInterfaceType]
     ) -> GraphQLFieldMap:
-        old_field_map = type_.fields
         new_field_map = {
             field_name: GraphQLField(
                 cast(GraphQLObjectType, extend_type(field.type)),
@@ -407,7 +405,7 @@ def extend_field_map(
                 ast_node=field.ast_node,
                 resolve=field.resolve,
             )
-            for field_name, field in old_field_map.items()
+            for field_name, field in type_.fields.items()
         }
 
         # If there are any extensions to the fields, apply those here.

graphql/validation/rules/values_of_correct_type.py

@@ -87,9 +87,8 @@ def enter_object_value(self, node: ObjectValueNode, *_args):
             self.is_valid_scalar(node)
             return self.SKIP  # Don't traverse further.
         # Ensure every required field exists.
-        input_fields = type_.fields
         field_node_map = {field.name.value: field for field in node.fields}
-        for field_name, field_def in input_fields.items():
+        for field_name, field_def in type_.fields.items():
             field_node = field_node_map.get(field_name)
             if not field_node and is_required_input_field(field_def):
                 field_type = field_def.type