Disable nesting-selector-no-missing-scoping-root for CSS-in-JS files (#657)

* Initial plan

* Disable nesting-selector-no-missing-scoping-root for .tsx files

The new stylelint version (16.26.1) via stylelint-config-recommended
introduces the nesting-selector-no-missing-scoping-root rule. This rule
doesn't understand CSS-in-JS patterns used by styled-components where &
is valid and refers to the component itself. Disabling this rule for
.tsx files fixes the CI test failures.

Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

* Add comment explaining nesting-selector-no-missing-scoping-root disable

Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jonrohan <54012+jonrohan@users.noreply.github.com>

Author: Copilot

index.js

@@ -149,6 +149,9 @@ export default {
         'length-zero-no-unit': null,
         'selector-max-type': null,
         'primer/colors': null,
+        // Disable nesting-selector-no-missing-scoping-root for CSS-in-JS
+        // In styled-components, the & selector is valid and refers to the component itself
+        'nesting-selector-no-missing-scoping-root': null,
       },
     },
     {