Downgrade to php7.4

[jonassiewertsen]

This PR does downgrade so Shiki does support PHP7.4 on top of PHP8 support.

To make the tests pass, I needed to remove some nice PHP8 syntax.

// Instead of this
$highlightedCode = Shiki::highlight($code, highlightLines: ['1', '2-4']);

// Downgrade to PHP 7.4
$highlightedCode = Shiki::highlight($code, null, null, ['1', '2-4']);

The good thing is, that someone who is using Shiki with PHP 8, can still use the nice PHP 8 syntax. It does only affect those, who wanna use it with PHP7.4.

• Tests do pass for PHP 7.4
• Readme has been updated

Motivation

It's a little dependency fun :-)

We are working on a PR to add TipTap 2 for Statamic. Statamic does support PHP 7.4 at the moment.
statamic/cms#6043

To upgrade, Statamic requires tiptap-php
In theory, it does support PHP 7.4

As tiptap does require shiki, shiki does require PHP 8 which does prevent it from beeing usable with PHP 7.4

[riasvdv]

Thanks!