feat: using right name for quantity_types

Author: a-bouth

src/ansys/dpf/gate/field_definition_grpcapi.py

@@ -107,6 +107,6 @@ def _modify_field_def(
         if name != None:
             request.name.string = name
         if quantity_type != None:
-            request.quantity_type = quantity_type
+            request.quantity_types.quantity_types = quantity_type
 
         _get_stub(fieldDef._server).Update(request)