Clippy 1.49.0 updates and dht persistence test fix (#2156)

## Issue Addressed

`test_dht_persistence` failing

## Proposed Changes

Bind `NetworkService::start` to an underscore prefixed variable rather than `_`.  `_` was causing it to be dropped immediately

This was failing 5/100 times before this update, but I haven't been able to get it to fail after updating it

Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/network/src/service/tests.rs

@@ -70,11 +70,9 @@ mod tests {
             // Create a new network service which implicitly gets dropped at the
             // end of the block.
 
-            let _ = NetworkService::start(beacon_chain.clone(), &config, executor)
+            let _network_service = NetworkService::start(beacon_chain.clone(), &config, executor)
                 .await
                 .unwrap();
-            // Allow the network task to spawn on the executor before shutting down.
-            tokio::time::sleep(std::time::Duration::from_secs(1)).await;
             drop(signal);
         });