chore: use os.availableParallelism()

This commit addresses an existing TODO in the code by moving
to the new os.availableParallelism() instead of os.cpus().length.

PR-URL: nodejs/node#45969
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
(cherry picked from commit fe5710effcb0b336853657e424da04407b0e49ad)

Author: cjihrig

lib/internal/test_runner/test.js

@@ -56,7 +56,7 @@ const {
 } = require('#internal/validators')
 const { setTimeout } = require('#timers/promises')
 const { TIMEOUT_MAX } = require('#internal/timers')
-const { cpus } = require('os')
+const { cpus, availableParallelism } = require('os')
 const { bigint: hrtime } = process.hrtime
 const kCallbackAndPromisePresent = 'callbackAndPromisePresent'
 const kCancelledByParent = 'cancelledByParent'
@@ -205,7 +205,9 @@ class Test extends AsyncResource {
 
       case 'boolean':
         if (concurrency) {
-          this.concurrency = parent === null ? MathMax(cpus().length - 1, 1) : Infinity
+          this.concurrency = parent === null
+            ? MathMax((typeof availableParallelism === 'undefined' ? cpus().length : availableParallelism()) - 1, 1)
+            : Infinity
         } else {
           this.concurrency = 1
         }