Hypercorn, however, supports the h2c HTTP/1.1 to HTTP/2 upgrade process. This allows a client to send a HTTP/1.1 request with a Upgrade: h2c header that results in the connection being upgraded to HTTP/2.

It does not work in latest version.

tried with curl --http2 http://url:port/path and throw exception.
tried with --http2-prior-knowledge and it works.
tried with Java JDK11 httpclient, and it downgrade to HTTP 1.1

so current only support direct http2 mode.

Please fix this.