[dev-overlay] Fix stacking order of highlighted line (#77189)

Author: raunofreiberg

packages/next/src/client/components/react-dev-overlay/ui/components/code-frame/code-frame.tsx

@@ -176,6 +176,7 @@ export const CODE_FRAME_STYLES = `
 
   [data-nextjs-codeframe-line][data-nextjs-codeframe-line--errored="true"] {
     position: relative;
+    isolation: isolate;
 
     > span { 
       position: relative;