doc: fix callback example import in fs documentation

[Rawal27]

Summary

The CommonJS example in the "Ordering of callback and promise-based operations"
section demonstrates callback-based usage but imports rename and stat
from node:fs/promises.

Since callback-based APIs are provided by node:fs, the example should
import from node:fs instead.

This change aligns the CommonJS example with the equivalent ESM example
and the callback API being demonstrated.

[Rawal27]

Hi, just checking in on this PR. All CI checks are passing, and the review was approved a while ago. Please let me know if there's anything else needed from my side. Thanks!

[nodejs-github-bot]

Landed in 23c6db5