message: Fix mutability lint warning.
diff: @@ -260,7 +260,7 @@ async fn propose_and_finalize(
  // The block validator returns true: The deploys in the block are valid. That completes our
  // requirements for the proposed block. The era supervisor announces that it has passed the
  // proposed block to the consensus protocol.
  - let mut effects = handle(es, rv_event);
  + let effects = handle(es, rv_event);
  assert!(effects.is_empty());
  // Node 1 now sends us another message that is sufficient for the protocol to finalize the
  