fix(wallet) serializing type for collectibles settings to backend

It seems `%*` operator we use in the `rpc` generics doesn't use the
`serializedFieldName` marker and `type` was serialized as `itemType`
and value the enum name instead of `type` and integer value

Updates: #13971

src/backend/collectibles_types.nim

@@ -451,3 +451,10 @@ proc fromJson*(t: JsonNode, T: typedesc[CollectiblePreferences]): CollectiblePre
   discard t.getProp("key", result.key)
   discard t.getProp("position", result.position)
   discard t.getProp("visible", result.visible)
+
+proc `%`*(cp: CollectiblePreferences): JsonNode {.inline.} =
+  result = newJObject()
+  result["type"] = %int(cp.itemType)
+  result["key"] = %cp.key
+  result["position"] = %cp.position
+  result["visible"] = %cp.visible