MassTransit: Send performance is degraded

Is this a bug report?

Yes

Can you also reproduce the problem with the latest version?

Yes, the problem exists with the latest version, but not with v7.3.1

Environment

1. Dotnet version: NET6
2. Operating system: Win10
3. IDE (Rider, VS Code, Visual Studio): Visual Studio 2022

Steps to Reproduce

1. Write a test program to produce n items of messages to a queue
2. Measure time
3. Calculate throughput

Expected Behavior

Throughput should not be degraded with the newest version

Actual Behavior

Throughput is massively degraded with the newest version

Masstransit v7.3.1
10000 items in 00:00:01.1654773, throughput=8580 m/s

Masstransit v8.0.6
10000 items in 00:00:27.8208227, throughput=359 m/s

Reproducible Demo

https://gist.github.com/mbendtsen/80b98ee670e4ea102b668ebbbc5f4456

    [Fact]
    public async Task RawMasstransit_Producer()
    {
        // Setup
        IBusControl busControl = serviceProvier.GetRequiredService<IBusControl>();

        const int itemCount = 10000;

        var messages = Enumerable.Repeat(new Message(), itemCount);

        // Exercise
        Stopwatch sp = Stopwatch.StartNew();

        var uri = new Uri($"queue:test-queue");
        var endpoint = await busControl.GetSendEndpoint(uri);
        await endpoint.SendBatch(messages);
        sp.Stop();

        // Verify
        double throughput = itemCount / sp.Elapsed.TotalSeconds;

        output.WriteLine($"{itemCount} items in {sp.Elapsed:c}, throughput={throughput:#} m/s");
    }