fix(NcDateTimePicker): correct button icon color

[pallavibakale]

☑️ Resolves

• Fixes 8488

🖼️ Screenshots

🏚️ Before | 🏡 After
|

B | A

🚧 Tasks

• Changed the color of the bottom button to make it visible

🏁 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 54.03%. Comparing base (28057a8) to head (553c83b).
⚠️ Report is 40 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8632   +/-   ##
=======================================
  Coverage   54.03%   54.03%           
=======================================
  Files         106      106           
  Lines        3479     3479           
  Branches     1008     1008           
=======================================
  Hits         1880     1880           
  Misses       1355     1355           
  Partials      244      244           

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