chore: improve beacon api example (#9660)

examples/beacon-api-sidecar-fetcher/src/main.rs

@@ -28,7 +28,7 @@ pub mod mined_sidecar;
 
 fn main() {
     Cli::<BeaconSidecarConfig>::parse()
-        .run(|builder, args| async move {
+        .run(|builder, beacon_config| async move {
             // launch the node
             let NodeHandle { node, node_exit_future } =
                 builder.node(EthereumNode::default()).launch().await?;
@@ -38,10 +38,11 @@ fn main() {
 
             let pool = node.pool.clone();
 
+            node.task_executor.spawn(async move {
                 let mut sidecar_stream = MinedSidecarStream {
                     events: notifications,
                     pool,
-                beacon_config: args,
+                    beacon_config,
                     client: reqwest::Client::new(),
                     pending_requests: FuturesUnordered::new(),
                     queued_actions: VecDeque::new(),
@@ -59,6 +60,8 @@ fn main() {
                         }
                     }
                 }
+            });
+
             node_exit_future.await
         })
         .unwrap();