fix: Update unkit/fetch package to use unjs/ofetch

[shinGangan]

🔗 Linked issue

❓ Type of change

• [x] 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• [ ] 🐞 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)
• [x] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

The unjs/ohmyfetch used in unkit/fetch was updated to unjs/ofetch. So, the following modifications fixed.

• add unjs/ofetch
• remove ohmyfetch
• rewrote ohmyfetch to ofetch in README.md.

📝 Checklist

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

[shinGangan]

Hi @pi0 .

I would appreciate it if you could approve the workflows and review when you have time.

• actions: https://github.com/unjs/unkit/actions/runs/7399485408