test: http2 connectionListener reject client

This code change modifies connectionListener tests to cover test case
where this.emit('unknownProtocol', socket) returns false

PR-URL: #16080
Ref: #14985
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>

test/parallel/test-http2-https-fallback.js

@@ -111,9 +111,9 @@ function onSession(session) {
     common.mustCall(onRequest)
   );
 
-  server.on('unknownProtocol', common.mustCall((socket) => {
+  server.once('unknownProtocol', common.mustCall((socket) => {
     socket.destroy();
-  }, 2));
+  }));
 
   server.listen(0);