Wait, what? If the government source is public domain, OSM (or anyone else) can take it and derive from it and can then impose whatever license OSM wants, including an attribution requirement. Did you mean the other way around?

Actually OSM's license is so weak on the attribution it requires, that OSM does not ingest CC-BY data, because OSM believes their further distribution would not satisfy CC-BY's attribution requirement.

https://osmfoundation.org/wiki/Licence/Licence_Compatibility