Add "no global scoped selector" rule for CSS Modules (#414)

* `npm i stylelint-css-modules-no-global-scoped-selector --force`

* Enable rule

* Add explicit `override` to `package.json`

* Add disable to fixture CSS

* Create clean-ads-work.md

.changeset/clean-ads-work.md

@@ -0,0 +1,5 @@
+---
+"@primer/stylelint-config": minor
+---
+
+Enable `css-modules/no-global-scoped-selector` rule for CSS Modules

__tests__/__fixtures__/good/example.module.css

@@ -3,6 +3,7 @@
   overflow: hidden;
 }
 
+/* stylelint-disable-next-line css-modules/no-global-scoped-selector */
 :root {
   --offset: -500px;
 }

index.js

@@ -178,6 +178,7 @@ export default {
     },
     {
       files: ['**/*.module.css'],
+      plugins: ['stylelint-css-modules-no-global-scoped-selector'],
       rules: {
         'property-no-unknown': [
           true,
@@ -202,6 +203,7 @@ export default {
             ignoreFunctions: ['global'],
           },
         ],
+        'css-modules/no-global-scoped-selector': true,
         // temporarily disabiling Primer plugins while we work on upgrades https://github.com/github/primer/issues/3165
         'primer/spacing': null,
         'primer/borders': null,