Fix Rust beta compiler errors (1.77) (#5180)

* Lint fixes

* More fixes for beta compiler.

* Format fixes

* Move `#[allow(dead_code)]` to field level.

* Remove old comment.

* Update beacon_node/execution_layer/src/test_utils/mod.rs

Co-authored-by: João Oliveira <hello@jxs.pt>

* remove duplicate line

beacon_node/network/src/subnet_service/tests/mod.rs

@@ -253,7 +253,7 @@ mod attestation_service {
             &attestation_service.beacon_chain.spec,
         )
         .unwrap();
-        let expected = vec![
+        let expected = [
             SubnetServiceMessage::Subscribe(Subnet::Attestation(subnet_id)),
             SubnetServiceMessage::Unsubscribe(Subnet::Attestation(subnet_id)),
         ];