AppNavigationHeaderDatePicker: adjust border radius

[GVodyanov]

Fix #6144

A	B

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 24.01%. Comparing base (7893c95) to head (cf59086).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #6161   +/-   ##
=========================================
  Coverage     24.01%   24.01%           
  Complexity      457      457           
=========================================
  Files           247      247           
  Lines         11578    11578           
  Branches       2185     2185           
=========================================
  Hits           2780     2780           
+ Misses         8484     8483    -1     
- Partials        314      315    +1     

Flag	Coverage Δ
javascript	15.49% <ø> (ø)
php	59.56% <ø> (ø)

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