test_runner: 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#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>

lib/internal/test_runner/test.js

@@ -53,7 +53,7 @@ const {
 } = require('internal/validators');
 const { setTimeout } = require('timers/promises');
 const { TIMEOUT_MAX } = require('internal/timers');
-const { cpus } = require('os');
+const { availableParallelism } = require('os');
 const { bigint: hrtime } = process.hrtime;
 const kCallbackAndPromisePresent = 'callbackAndPromisePresent';
 const kCancelledByParent = 'cancelledByParent';
@@ -216,8 +216,8 @@ class Test extends AsyncResource {
 
       case 'boolean':
         if (concurrency) {
-          // TODO(cjihrig): Use uv_available_parallelism() once it lands.
-          this.concurrency = parent === null ? MathMax(cpus().length - 1, 1) : Infinity;
+          this.concurrency = parent === null ?
+            MathMax(availableParallelism() - 1, 1) : Infinity;
         } else {
           this.concurrency = 1;
         }