refactor(iota-core): silence unused variable warning (#3918)

Co-authored-by: Bing-Yang <[email protected]>
Co-authored-by: Thibault Martinez <[email protected]>

crates/iota-core/src/checkpoints/mod.rs

@@ -1104,13 +1104,13 @@ impl CheckpointBuilder {
 
         let _scope = monitored_scope("CheckpointBuilder::causal_sort");
         let mut sorted: Vec<TransactionEffects> = Vec::with_capacity(unsorted.len() + 1);
-        if let Some((ccp_digest, ccp_effects)) = consensus_commit_prologue {
+        if let Some((_ccp_digest, ccp_effects)) = consensus_commit_prologue {
             #[cfg(debug_assertions)]
             {
                 // When consensus_commit_prologue is extracted, it should not be included in the
                 // `unsorted`.
                 for tx in unsorted.iter() {
-                    assert!(tx.transaction_digest() != &ccp_digest);
+                    assert!(tx.transaction_digest() != &_ccp_digest);
                 }
             }
             sorted.push(ccp_effects);