Why does my very simple C# program leak 890MB of RAM?

using System.IO;
using System.Net.Http;

Console.WriteLine("Hello, World! v3");

static async Task GetRequest(string url)
{
    using (var httpClient = new HttpClient())
    {
        try
        {
            using (var response = await httpClient.GetAsync(url))
            {
                var stream = await response.Content.ReadAsStreamAsync();
                await stream.CopyToAsync(Stream.Null);
            }
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("\nException Caught!");
            Console.WriteLine("Message :{0} ", e.Message);
        }
    }
}


const string URL_TO_GET = "https://speed.cloudflare.com/__down?measId=0&bytes=50000000";
List<Task> tasks = new List<Task>();
for (int i = 0; i < 8; i++)
{
    tasks.Add(GetRequest(URL_TO_GET));
}
await Task.WhenAll(tasks);

Console.WriteLine("Work Complete!");