Downgrade Sass to 1.77.5 and fix as many deprecations as possible

.github/workflows/pull-request.yml

@@ -89,6 +89,7 @@ jobs:
         run: npm run test:visual
 
       - name: Save backstop report
+        if: ${{ always() }}
         uses: actions/upload-artifact@v4
         with:
           name: Backstop report

gulpfile.js

@@ -5,7 +5,7 @@ const postcss = require('gulp-postcss')
 const rename = require('gulp-rename')
 const gulpSass = require('gulp-sass')
 const terser = require('gulp-terser')
-const dartSass = require('sass')
+const dartSass = require('sass-embedded')
 const webpack = require('webpack-stream')
 
 const { version } = require('./package.json')