Correct clippy lint identified upon rebase

common/db/src/parity_db.rs

@@ -4,6 +4,7 @@ pub use ::parity_db::{Options, Db as ParityDb};
 
 use crate::*;
 
+#[must_use]
 pub struct Transaction<'a>(&'a Arc<ParityDb>, Vec<(u8, Vec<u8>, Option<Vec<u8>>)>);
 
 impl Get for Transaction<'_> {

common/db/src/rocks.rs

@@ -7,6 +7,7 @@ use rocksdb::{
 
 use crate::*;
 
+#[must_use]
 pub struct Transaction<'a, T: ThreadMode>(
   RocksTransaction<'a, OptimisticTransactionDB<T>>,
   &'a OptimisticTransactionDB<T>,