doc: mark process.nextTick legacy

PR-URL: #51280
Refs: #51156
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Paolo Insogna <paolo@cowtech.it>

doc/api/process.md

@@ -2701,6 +2701,9 @@ console.log(memoryUsage.rss());
 <!-- YAML
 added: v0.1.26
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/51280
+    description: Changed stability to Legacy.
   - version: v18.0.0
     pr-url: https://github.com/nodejs/node/pull/41678
     description: Passing an invalid callback to the `callback` argument
@@ -2711,6 +2714,8 @@ changes:
     description: Additional arguments after `callback` are now supported.
 -->
 
+> Stability: 3 - Legacy: Use [`queueMicrotask()`][] instead.
+
 * `callback` {Function}
 * `...args` {any} Additional arguments to pass when invoking the `callback`