storcon: don't log a heartbeat error during shutdown

storage_controller/src/service.rs

@@ -1046,6 +1046,9 @@ impl Service {
                             // on a snapshot of the nodes.
                             tracing::info!("Node {} was not found after heartbeat round", node_id);
                         }
+                        Err(ApiError::ShuttingDown) => {
+                            // No-op: we're shutting down, no need to try and update any nodes' statuses
+                        }
                         Err(err) => {
                             // Transition to active involves reconciling: if a node responds to a heartbeat then
                             // becomes unavailable again, we may get an error here.