Fixed PHP 8.1 compatibility of the requirement checker

[GrahamCampbell]

It looks like #557 wasn't enough to fix this. This file needs updating too.

[freekmurze]

This PR seems to fix PHP 8.1 compatibility. 👍

I'll just create a fork with this fix and use that until it is merged in.

[GrahamCampbell]

I am using my fork. ;)

[Jeckerson]

@theofidry ping

[jakzal]

The build failure:

atal error: During inheritance of IteratorAggregate: Uncaught ErrorException: Return type of Symfony\Component\Console\Helper\HelperSet::getIterator() should either be compatible with IteratorAggregate::getIterator(): Traversable, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /home/runner/work/box/box/vendor/symfony/console/Helper/HelperSet.php:103
#0 /home/runner/work/box/box/vendor/symfony/console/Helper/HelperSet.php(22): KevinGH\Box\{closure}()

will probably be fixed by symfony/symfony#42260

[jakzal]

The above fix was released in Symfony 4.4.30, 5.3.7, 5.4.0, and 6.0.0.

[theofidry]

Thank you. Will update the Symfony dependencies shortly