fix(NcAppNavigationSettings): border radius of toggle button

[st3iny]

☑️ Resolves

• Fix https://github.com/nextcloud-libraries/nextcloud-vue/issues/5764

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• [ ] ...

🏁 Checklist

• [ ] ⛑️ Tests are included or are not applicable
• [ ] 📘 Component documentation has been extended, updated or is not applicable
• [ ] 3️⃣ Backport to next requested with a Vue 3 upgrade