[migration] Improve update of in-memory schema during 3.18 CWAttribute.defaultval change We weren't updating the schema properly so a bunch of structures still had the old rdef with 'String' as object. That caused failures to add new attributes later in the migration as their default value would be a Binary object but the schema would expect a String. Closes #3683640

sync_schema_props_perms('cw_source', syncprops=False)
if schema['BigInt'].eid is None:
    add_entity_type('BigInt')