fix types

Author: Schniz

packages/next/server/next-server.ts

@@ -1415,15 +1415,15 @@ function enhanceIncomingMessage<T extends IncomingMessage>(
   return new Proxy<T>(base, {
     get(target, name) {
       if (name in stream) {
-        const v = stream[name]
+        const v = stream[name as keyof NodeStreams.Readable]
         if (typeof v === 'function') {
           return v.bind(stream)
         } else {
           return v
         }
       }
 
-      return target[name]
+      return target[name as keyof T]
     },
   })
 }