phpcompatibility/php-compatibility dependency is not compatible with PHP 8

[aadmathijssen]

This package depends on version "^9.3" of the phpcompatibility/php-compatibility dependency.

This includes the latest stable version 9.3.5, which is now more than 3 years old. As a result, PHP 8 is not fully supported. This introduces lots of missed cases, but can also introduces false positives.

For example, consider this backed enum code:

<?php

enum Foo: string
{
    case Bar = 'bar';

    public function getValue(): string
    {
        return $this->value;
    }
}

This generates an error regarding the use of $this:

$ vendor/bin/phpcs --standard=PHPCompatibility --runtime-set testVersion 8.1 file.php

FILE: /path/to/file.php
-----------------------------------------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
-----------------------------------------------------------------------------------------------------
 9 | ERROR | "$this" can no longer be used in a plain function or method since PHP 7.1.
-----------------------------------------------------------------------------------------------------

A temporary workaround is to make use of the latest dev-develop version of this dependency, which has much better support for PHP 8.
To include this in a project that uses the ISAAC PHP_CodeSniffer Standard, you can upgrade the dependency

$ composer require --dev --with-all-dependencies "phpcompatibility/php-compatibility:dev-develop as 9.3.5"

However, I am hesitant to create a PR to update phpcompatibility/php-compatibility to dev-develop, as I only want to depend on stable package version.