fix: ignores WebSocket connection with same sid after upgrade

[Totodore]

The second websocket created after an upgrade should gracefully close and not throw an error as specified in the official implementation. Moreover in the same test for the socket.io test suite the implementation wait for the second websocket to gracefully close.

Here is an example of engine.io server which fails at validating this test:

const engine = require('engine.io');
const server = engine.listen(3000, {
    pingInterval: 300,
    pingTimeout: 200
});

server.on('connection', socket => {
    socket.on('message', data => {
        socket.send(data);
    });
});

It would be nice to be able to use a separate engine.io test suite in CI for our rust server implementation socketioxide.

Closes socketio/socket.io-protocol#29
Closes Totodore/socketioxide#15

[Totodore]

@darrachequesne even the new v3 test-suite waits for a close event and not an error event.

[darrachequesne]

Good catch, thanks!