fix(test-utils): export from core playwright package

[danielroe]

🔗 Linked issue

❓ 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)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Playwright recently deprecated having both playwright and @playwright/test installed, which means that users with just @playwright/test dependency - who cannot install playwright any more - nuxt test utils will fail to work.

Instead, we can import the core (browserless) playwright implementation from playwright-core.

📝 Checklist

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

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