fix(nuxt): refetch both undefined/null values in useAsyncData

[warflash]

🔗 Linked issue

Resolves #23349
Resolves #22696

❓ 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)

📚 Description

This ensures nuxt payload data is checked against null and undefined values in the (hopefully) least breaking way possible.
When useNuxtData is called before a client side useAsyncData call is resolved, useNuxtDatawill set the value of the key to null. hasCachedData so far only checked for undefined values so null would pass and be returned, both for the useAsyncData and useNuxtData.
I feel like this is not the cleanest way to go about this, setting they key to undefined like clearNuxtData does might be more concise. However then the return signature of useNuxtData => <DataT | undefined> might break existing user logic.

📝 Checklist

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

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[danielroe]

Would you be able to add a regression test to cover the situation in the linked issue? 🙏

We can then look at fixing the currently failing tests.