SCSS-PHP no longer supports PHP 7.4

[eliot-akira]

From this commit comment by @nicolas-jaussaud:

the minimal php version for SCSS-PHP is now 8.1

Are we also switching to php 8.1 and above as the minimal version for template-system and the associated projects, or should we still try to correct anything we encounter that is not php 7.4 compatible?

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According to the WordPress usage statistics, 43% of users are still on PHP 7.4. So we should maintain compatibility until more people switch over.

From the recent Git history in SCSS-PHP, they're modernizing a lot of the code. We can fork it but I'm afraid of the effort it would take to keep an eye on every upstream change and modify it for PHP 7.4 (which might not be technically possible in some cases).

For now, I suppose we need to revert the Sass compiler to the latest backward-compatible version of SCSS-PHP (right before that commit you linked to).

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There are some basic tests for the Sass compiler, which get run on both PHP 8.2 and 7.4. They're all passing even after the upgrade to SCSS-PHP 1.12.1, and I don't see any PHP syntax errors or warnings.

So maybe we can "freeze" it at this point, until we figure out how to move away from SCSS-PHP altogether:

• Use browser build of Sass or PostCSS compiler #88