chore(s2n-quic-dc): increase the wait for async background handshake

Author: boquan-fang

dc/s2n-quic-dc/src/stream/tests/restart.rs

@@ -143,7 +143,7 @@ impl Harness {
         );
 
         // Wait for the asynchronous background handshake.
-        tokio::time::sleep(Duration::from_millis(50)).await;
+        tokio::time::sleep(Duration::from_secs(2)).await;
 
         check_stream(&context, bidirectional, sleep_before_shutdown)
             .instrument(info_span!("four"))