docs: update placeholder attributes in <NuxtImg /> example

[Dino-Kupinic]

🔗 Linked issue

resolves #2053
resolves #2073

❓ 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

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@nuxt/image@2074

commit: 4a3a60d

[danielroe]

thank you!

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 6.99%. Comparing base (5808397) to head (4a3a60d).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2074   +/-   ##
=====================================
  Coverage   6.99%   6.99%           
=====================================
  Files         78      78           
  Lines       3629    3629           
  Branches     140     140           
=====================================
  Hits         254     254           
  Misses      3326    3326           
  Partials      49      49           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.