docs: update seo and meta page

[dosstx]

Add the await keyword before useFetch. useFetch is an asynchronous function that returns a Promise, so you need to use the await keyword to wait for the Promise to resolve before assigning its value to the post variable. This ensures that the data is available before it is used in the useServerSeoMeta function.

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❓ Type of change

• 📖 Documentation (updates to the documentation, readme or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

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• I have linked an issue or discussion.
• I have updated the documentation accordingly.

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[dosstx]

On second thought probably don't need to use AWAIT here since it's a computed getter.

[Atinux]

Thank you @dosstx

Actually I thought about it as well, but for the useSeoMeta example, I believe useFetch is not the right example.

Will update your PR to improve the example.

See my demo on https://stackblitz.com/edit/github-vlzrtd?file=app.vue

[Atinux]

Preview link: https://nuxt.com/docs/getting-started/seo-meta?preview=83ceb1ab7b8ae2614a7d3b70bc1eea07