schemas/fields: Explicitly convert `serialize_polygon()` return value to a `list`
schemas/fields: Explicitly convert `serialize_polygon()` return value to a `list`

RBE-Avionik/skylines,Turbo87/skylines,Harry-R/skylines,skylines-project/skylines,skylines-project/skylines,RBE-Avionik/skylines,skylines-project/skylines,Turbo87/skylines,Harry-R/skylines,Turbo87/skylines,Turbo87/skylines,RBE-Avionik/skylines,RBE-Avionik/skylines,skylines-project/skylines,Harry-R/skylines,Harry-R/skylines