chore: fix typescript error (#734)

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### ❓ Type of change

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- [ ] 📖 Documentation (updates to the documentation or readme)
- [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
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### 📚 Description

Fixes the CI errors.

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packages/storybook-addon/src/preview.ts

@@ -42,6 +42,7 @@ setup(async (vueApp, storyContext) => {
   }
 
   // Provide the config of the Nuxt app
+  // @ts-expect-error internal Nuxt property
   window.__NUXT__ = {
     serverRendered: false,
     config: {