[stable8] fix(NcAppSettingsDialog): set box-sizing: border-box for the new design

[ShGKme]

☑️ Resolves

• Ref: feat(Settings): redesign to new vue components nextcloud/calendar#7682 (comment)

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 2️⃣ Backport to stable8 for maintained Vue 2 version or not applicable

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.38%. Comparing base (c5ee4b7) to head (39416c7).
⚠️ Report is 13 commits behind head on stable8.

Additional details and impacted files

@@             Coverage Diff             @@
##           stable8    #7888      +/-   ##
===========================================
+ Coverage    45.08%   45.38%   +0.30%     
===========================================
  Files          191      192       +1     
  Lines         4749     4768      +19     
  Branches      1226     1171      -55     
===========================================
+ Hits          2141     2164      +23     
+ Misses        2512     2510       -2     
+ Partials        96       94       -2     

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[Antreesy]

LGTM for me, better to test for Vue 2 apps

[susnux]

name is a bit weird but ok

[ShGKme]

name is a bit weird but ok

You can make a suggestion for the name