Validate IncidentUpdate's incident_type field against the retrieved i…

…ncident type. (#4699)

* Validate IncidentUpdate's incident_type field against the retrieved incident_type.

* Fixes incident_type swap.

src/dispatch/incident/service.py

@@ -366,7 +366,7 @@ def update(*, db_session, incident: Incident, incident_in: IncidentUpdate) -> In
         )
 
     # Update total incident reponse cost if incident type has changed.
-    if incident_in.incident_type.id != incident.incident_type.id:
+    if incident_type.id != incident.incident_type.id:
         incident_cost_service.update_incident_response_cost(
             incident_id=incident.id, db_session=db_session
         )