fix attribute expiration_date_warned

Author: wurstbrot

src/main/java/io/securecodebox/persistence/defectdojo/models/RiskAcceptance.java

@@ -55,7 +55,7 @@ public class RiskAcceptance extends DefectDojoModel {
   String expiration_date;
 
   @JsonProperty
-  Long expiration_date_warned;
+  LocalDateTime expiration_date_warned;
 
   @JsonProperty
   Boolean expiration_date_handled;