fix(vitest-environment): respect custom app.baseURL in manifest path

[danielroe]

resolves #1212

🔗 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)
• ✨ 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

I'd advise against using a custom baseURL in testing but this respects it if provided.

[pkg-pr-new]

Open in Stackblitz

npm i https://pkg.pr.new/@nuxt/test-utils@1213

commit: 8226c2c