message: add arbitrary setting for the diff of the block version
diff: @@ -257,6 +257,7 @@ mod tests {
  impl Arbitrary for SettingsDiff {
  fn arbitrary<G: Gen>(g: &mut G) -> SettingsDiff {
  SettingsDiff {
  + block_version: ValueDiff::None,
  block_id: ValueDiff::Replace(Arbitrary::arbitrary(g), Arbitrary::arbitrary(g)),
  bootstrap_key_slots_percentage: ValueDiff::Replace(
  Arbitrary::arbitrary(g),
  