Add some debugging to a TCP test (#12890)

Attempting to help diagnose the spurious failure that cropped up in #12864.

Closes #12864

Author: alexcrichton

crates/test-programs/src/bin/p3_sockets_tcp_streams.rs

@@ -102,7 +102,10 @@ async fn test_tcp_send_drops_stream_when_remote_shutdown(family: IpAddressFamily
         }
 
         let result = client.send_result.await;
-        assert!(matches!(result, Err(ErrorCode::ConnectionBroken)));
+        assert!(
+            matches!(result, Err(ErrorCode::ConnectionBroken)),
+            "unexpected error {result:?}",
+        );
     })
     .await;
 }