fix(fastify): address deprecation warning

Author: kamilmysliwiec

benchmarks/fastify.js

@@ -2,4 +2,6 @@
 
 const fastify = require('fastify')();
 fastify.get('/', async (req, reply) => reply.send('Hello world'));
-fastify.listen(3000);
+fastify.listen({
+  port: 3000
+});

packages/platform-fastify/adapters/fastify-adapter.ts

@@ -226,10 +226,12 @@ export class FastifyAdapter<
   public listen(port: string | number, ...args: any[]): void {
     const isFirstArgTypeofFunction = typeof args[0] === 'function';
     const callback = isFirstArgTypeofFunction ? args[0] : args[1];
-    const options = {
+    let options: Record<string, any> = {
       port: +port,
-      host: isFirstArgTypeofFunction ? undefined : args[0],
     };
+    if (!isFirstArgTypeofFunction) {
+      options.host = args[0];
+    }
     return this.instance.listen(options, callback);
   }