fix double finalize warning

[xlc]

Followup of #1438

Currently running cargo run --features with-mandala-runtime -- --dev will result such warning

Possible safety violation: attempted to re-finalize last finalized block 0xd30a32549274fff8092dd3e6c1f5cc640ac09eff876d34c9b825aab9ec95b757     

Need to find a way to avoid it.

[xlc]

This should help https://github.com/paritytech/substrate/pull/12106