Improve contrast of sidebar toggle icon

[karenrasmussen]

This pull request makes a minor UI update to the Toolbar component. The change adjusts the default icon color to use a slightly darker shade of grey, improving visual contrast.

• Updated the Toolbar button's default text color from text-grey-5 to text-grey-6 for better contrast and consistency.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.50%. Comparing base (cd48709) to head (8ed3087).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7484   +/-   ##
=======================================
  Coverage   99.50%   99.50%           
=======================================
  Files         271      271           
  Lines       11076    11076           
  Branches     2666     2666           
=======================================
  Hits        11021    11021           
  Misses         55       55           

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