ci: Check for use of SCSS random() (#40666)

Normal CSS can't do random numbers. SCSS has a `random()` function,
which produces random values in the output CSS. Unfortunately this makes
the built CSS change for each build, which means that every PR merged
will require a Simple deploy. To avoid this, add a CI check looking for
calls to the function in all `.scss` files.

Also do the same for `unique-id()`.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/12400572435

Upstream-Ref: Automattic/jetpack@3ed576d

CHANGELOG.md

@@ -28,6 +28,7 @@ This is an alpha version! The changes listed here are not final.
 - Fix migration key fetch failing when DIY migration page is reloaded
 - Gutenberg 19.8.0 hotfix: don't show the template-locked rendering mode for pages
 - Holiday Snow: do not display on p2s.
+- Holiday snow: Replace SCSS `random()` with pregenerated arrays of random numbers to make builds reproducable.
 - Load WPCOM sidebar notice async
 - Restore visited button color in themes.php to Core's default
 - Starter page templates: correctly insert the pattern to the Content block when rendering mode is template-locked

src/build/holiday-snow/holiday-snow.asset.php

@@ -1 +1 @@
-<?php return array('dependencies' => array(), 'version' => '245c23ca920a321a84cb');
+<?php return array('dependencies' => array(), 'version' => '9d60d5e59cb26f8f3085');