MuxedStreamNamespacedPodExecAsync doesn't open a V5 WebSocket #1946

Describe the bug
When requesting a StreamDemuxer using MuxedStreamNamespacedPodExecAsync with webSocketSubProtocol: WebSocketProtocol.V5BinaryWebsocketProtocol, it opens a v4 websocket instead

Kubernetes C# SDK Client Version
21.0.8

Server Kubernetes Version
1.36.1

Dotnet Runtime Version
net8

To Reproduce
Steps to reproduce the behavior:

• create a Kubernetes client
• create a helper pod with CoreV1.CreateNamespacedPodAsync
• request a MuxedStreamNamespacedPodExecAsync with webSocketSubProtocol = WebSocketProtocol.V5BinaryWebsocketProtocol

Expected behavior
Expect a websocket with protocol V5

KubeConfig
If applicable, add a KubeConfig file with secrets redacted.

Where do you run your app with Kubernetes SDK (please complete the following information):

• OS: Windows, with Kubernetes in Docker Desktop

Additional context
I am using ubuntu as the helper pod

I can get a V5 websocket using WebSocketNamespacedPodExecAsync and then create a StreamDemuxer like so:

    public async Task<IStreamDemuxer> MuxedStreamNamespacedPodExecAsync(
    string podName,
    string namespaceName,
    string containerName,
    IEnumerable<string> command,
    CancellationToken cancellationToken = default)
    {
        // Make our own StreamDemuxer from a websocket
        // since client.MuxedStreamNamespacedPodExecAsync does not properly open a V5 websocket
        var ws = await client.WebSocketNamespacedPodExecAsync(podName, namespaceName, command, containerName, tty: false, webSocketSubProtocol: WebSocketProtocol.V5BinaryWebsocketProtocol, cancellationToken: cancellationToken);

        if (ws.SubProtocol != WebSocketProtocol.V5BinaryWebsocketProtocol)
            throw new InvalidOperationException($"Expected Websocket protocol V5, but got {ws.SubProtocol}");

        return new StreamDemuxer(ws, StreamType.RemoteCommand, ownsSocket: true, supportsClose: true);
    }