chore: add @nowarn for ScalaTestEventMigration

Author: He-Pin

akka-serialization-jackson/src/test/scala/akka/serialization/jackson/ScalaTestEventMigration.scala

@@ -8,6 +8,8 @@ import com.fasterxml.jackson.databind.JsonNode
 import com.fasterxml.jackson.databind.node.IntNode
 import com.fasterxml.jackson.databind.node.ObjectNode
 
+import scala.annotation.nowarn
+
 object ScalaTestEventMigration {
   def upcastV1ToV2(root: ObjectNode): ObjectNode = {
     root.set[JsonNode]("field1V2", root.get("field1"))
@@ -17,15 +19,15 @@ object ScalaTestEventMigration {
   }
 
   def upcastV2ToV3(root: ObjectNode): ObjectNode = {
-    root.set("field3", root.get("field2"))
+    root.set("field3", root.get("field2")): @nowarn
     root.remove("field2")
     root
   }
 
   def downcastV3ToV2(root: ObjectNode) = {
     // downcast the V3 representation to the V2 representation. A field
     // is renamed.
-    root.set("field2", root.get("field3"))
+    root.set("field2", root.get("field3")): @nowarn
     root.remove("field3")
     root
   }