Make sure staking migration code runs only for version = 2_0_0

frame/staking/src/lib.rs

@@ -1246,8 +1246,12 @@ decl_module! {
  fn on_runtime_upgrade() -> Weight {
  // For Kusama the type hasn't actually changed as Moment was u64 and was the number of
  // millisecond since unix epoch.
- StorageVersion::put(Releases::V3_0_0);
- Self::migrate_last_reward_to_claimed_rewards();
+ StorageVersion::mutate(|v| {
+ if matches!(v, Releases::V2_0_0) {
+ Self::migrate_last_reward_to_claimed_rewards();
+ }
+ *v = Releases::V3_0_0;
+ });
  0
  }