Program never exits when cancelling the `StreamSubscription` of `WebSocketChannel.stream`

The following program will never exit:

import 'package:web_socket_channel/web_socket_channel.dart';

void main() async {
  final conn = WebSocketChannel.connect(Uri.parse('ws://localhost:8000/ws'));

  final sub = conn.stream.listen(null);

  await Future.delayed(Duration(seconds: 2));
  await sub.cancel(); // <~~~ when commenting this out, the program exits normally (removing await won't change a thing)
  await conn.sink.close(1000, 'normal closure');
}

To reproduce:

run the following series of commands:

dart create websocket_channel_bug
cd websocket_channel_bug
dart pub add web_socket_channel shelf_web_socket shelf shelf_router 
touch bin/server.dart
touch bin/client.dart

add server code to bin/server.dart:

import 'dart:io';

import 'package:shelf/shelf.dart';
import 'package:shelf/shelf_io.dart';
import 'package:shelf_router/shelf_router.dart';
import 'package:shelf_web_socket/shelf_web_socket.dart';
import 'package:web_socket_channel/web_socket_channel.dart';

void main() {
final router = Router()
  ..get('/ws', webSocketHandler((WebSocketChannel conn) {
    conn.stream.listen((event) {
      print(event);
    });
  }));

final pipeline = Pipeline().addHandler(router);
serve(pipeline, InternetAddress.anyIPv4, 8000);
print('serving at localhost:8000');
}

add client code to bin/client.dart:

import 'package:web_socket_channel/web_socket_channel.dart';

void main() async {
final conn = WebSocketChannel.connect(Uri.parse('ws://localhost:8000/ws'));

final sub = conn.stream.listen(null);

await Future.delayed(Duration(seconds: 2));
await sub.cancel(); // <~~~ when commenting this out, the program exits normally 
await conn.sink.close(1000, 'normal closure');
}

in one terminal run:
```
dart run bin/server.dart
```
in another terminal run:
```
dart run bin/client.dart
```
The last program will never exit.

Additional info:

web_socket_channel: ^2.2.0
Dart SDK version: 2.17.6 (stable) (Tue Jul 12 12:54:37 2022 +0200) on "macos_x64"

dart-lang / web_socket_channel

Program never exits when cancelling the `StreamSubscription` of `WebSocketChannel.stream` #228

To reproduce:

The last program will never exit.