initialize the listener with a valid TLS config

The certificate doesn’t matter, since it is not validated anywehere
(yet), but we need to send something.

listener.go

 package libp2pquic
 
 import (
-	"crypto/tls"
 	"net"
 
 	pstore "github.com/libp2p/go-libp2p-peerstore"
 	tpt "github.com/libp2p/go-libp2p-transport"
+	testdata "github.com/lucas-clemente/quic-go/testdata"
 	quicconn "github.com/marten-seemann/quic-conn"
 	ma "github.com/multiformats/go-multiaddr"
 	manet "github.com/multiformats/go-multiaddr-net"
@@ -19,7 +19,9 @@ type listener struct {
 }
 
 func newListener(laddr ma.Multiaddr, peers pstore.Peerstore, transport tpt.Transport) (*listener, error) {
-	tlsConf := &tls.Config{}
+	// we need to provide a certificate here
+	// use the demo certificate from quic-go
+	tlsConf := testdata.GetTLSConfig()
 	network, host, err := manet.DialArgs(laddr)
 	if err != nil {
 		return nil, err