fix: only show Tailwind v4 warning when v4 is used

[cjpearson]

🔗 Linked issue

#983

❓ 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)
• ✨ 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

Check isTailwind4 before logging the warning so it won't be shown when using v3.

[netlify]

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Name	Link
🔨 Latest commit	365133b

[what-the-diff]

PR Summary

• Enhanced Warning Condition for Tailwind CSS
  The logic behind issuing warnings for Tailwind CSS has been improved. The updated condition now checks if Tailwind CSS version 4 is in use prior to issuing any warning. This enhancement provides more accuracy and relevancy in warnings, thereby improving the user experience.

[ineshbose]

You're an absolute angel. Part of having nightly-version users is to detect my silly mistakes here and there and help contribute for a stable release. Thank you for using nightly and report this ❤️