公式ページにちゃんとありました。
Laravel 8.x Laravel Sail　PHPバージョン

# For more information: https://laravel.com/docs/sail
version: '3'
services:
    laravel.test:
        build:
            context: ./docker/8.1
            dockerfile: Dockerfile
            args:
                WWWGROUP: '${WWWGROUP}'
        image: sail-8.1/app

Dockerを一回落として、起動します。

 $ docker-compose down
 $ docker-compose up -d
 $ docker-compose ps
 $ ./vendor/bin/sail php --version
 PHP 8.1.2 (cli) (built: Jan 24 2022 10:42:51) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.2, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.2, Copyright (c), by Zend Technologies
    with Xdebug v3.1.2, Copyright (c) 2002-2021, by Derick Rethans