fs: ensure consistency for mkdtemp in both fs and fs/promises

Port changes for mkdtemp from lib/fs.js to lib/internal/fs/promise.js,
ensuring consistent behavior.
Refs: #51078
PR-URL: #53776
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: LiviaMedeiros <livia@cirno.name>

Author: YieldRay

lib/internal/fs/promises.js

@@ -1179,15 +1179,8 @@ async function mkdtemp(prefix, options) {
 prefix=getValidatedPath(prefix,'prefix');
 warnOnNonPortableTemplate(prefix);
 
-letpath;
-if(typeofprefix==='string'){
-path=`${prefix}XXXXXX`;
-}else{
-path=Buffer.concat([prefix,Buffer.from('XXXXXX')]);
-}
-
 returnawaitPromisePrototypeThen(
-binding.mkdtemp(path,options.encoding,kUsePromises),
+binding.mkdtemp(prefix,options.encoding,kUsePromises),
 undefined,
 handleErrorFromBinding,
 );