Merge branch 'psi-never-extend-again' into 'master'

Disallow SCSS extend in stylelint config

See merge request gitlab-org/gitlab!71288

.stylelintrc

@@ -13,6 +13,7 @@
       "./scripts/frontend/stylelint/stylelint-utility-classes.js",
    ],
    "rules":{
+      "at-rule-disallowed-list": ["extend"],
       "max-nesting-depth": [
          3,
          {