source.json's type is string, not object

source.json is of type string, not of type object, this has always been correct:

https://github.com/folio-org/acq-models/blob/83966672ed65be84636951f504b9137df6c2ee0f/mod-orders-storage/schemas/source.json

It gets incorrectly linked as type object:

https://github.com/folio-org/acq-models/blob/83966672ed65be84636951f504b9137df6c2ee0f/mod-orders-storage/schemas/po_line.json#L236-L240

https://github.com/folio-org/acq-models/blob/83966672ed65be84636951f504b9137df6c2ee0f/mod-orders/schemas/composite_po_line.json#L239-L243

The wrong type is published in the API documentation: https://dev.folio.org/reference/api/

Solution: Fix wrong type.