fix: ignore clippy's directive as this thing looks like intended usage

Author: vsavchyn-dev

api/src/signer/mod.rs

@@ -556,6 +556,7 @@ impl Signer {
             .await
             .map_err(|e| SignerError::FetchNonceError(Box::new(e)))?;
 
+        #[allow(clippy::significant_drop_tightening)]
         let nonce = {
             let mut nonce_cache = self.nonce_cache.lock().await;
             let nonce = nonce_cache.entry((account_id, public_key)).or_default();