Making HTTP2 requests

I am attempting to test a local .NET Kestrel server which only accepts
http2 requests. However it seems that even when I specify --http2 it sends
http1 requests.

> curl --http2 -i http://localhost:5000/health
HTTP/1.1 400 Bad Request
Connection: close
Content-Type: text/plain
Content-Length: 56

An HTTP/1.x request was sent to an HTTP/2 only endpoint.

> curl --http2-prior-knowledge -i http://localhost:5000/health
HTTP/1.1 400 Bad Request
Connection: close
Content-Type: text/plain
Content-Length: 56

An HTTP/1.x request was sent to an HTTP/2 only endpoint.

This is the ASP.NET config I'm using (the default for Protocols is
HttpProtocols.Http1AndHttp2):

builder.WebHost
.ConfigureKestrel(serverOptions =>
{
    serverOptions.Listen(IPAddress.Any, 5000, listenOptions =>
    {
        listenOptions.Protocols = HttpProtocols.Http2;
    });

    serverOptions.Listen(IPAddress.Any, 5443, listenOptions =>
    {
        listenOptions.Protocols = HttpProtocols.Http2;
        listenOptions.UseHttps(certificate);
    });
})

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