Fix tests, restore Alpine tests, fix PHP 8.1+ deprecation warning

[mlocati]

Fix #35

[27pchrisl]

Hi @mlocati, I was checking out this very welcome PR with the code below that segfaults on PHP 8.2 on Ubuntu and MacOS. Was this a 8.2 compatibility fault that this PR will address or is it a different area of work?

<?php

$matrix = Tensor\Matrix::ones(2,2);
$matrix->inverse();

Thankyou!

[mlocati]

Was this a 8.2 compatibility fault that this PR will address or is it a different area of work?

Nope, I just fixed a couple of deprecation warnings about classes extending ArrayAccess / IteratorAggregate

[andrewdalpino]

Thank you @mlocati!