doc: add missing buffer in the stream/consumers import example

PR-URL: https://github.com/nodejs/node/pull/41961
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>

doc/api/webstreams.md

@@ -1380,6 +1380,7 @@ They are accessed using:
 import {
   arrayBuffer,
   blob,
+  buffer,
   json,
   text,
 } from 'node:stream/consumers';
@@ -1389,6 +1390,7 @@ import {
 const {
   arrayBuffer,
   blob,
+  buffer,
   json,
   text,
 } = require('stream/consumers');