ci: limit nuxt2 nightly build to nuxt org

[ineshbose]

🔗 Issue

nuxt2-nightly runs on forks of the nuxt/nuxt repository every night (and also fails - A branch or tag with the name '2.x' could not be found) and sending out an alert of fork owners, such as myself & over email at midnight, about the CI run. 😅

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 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)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Added condition to nightly job.

📝 Checklist

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

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[danielroe]

Thanks!