FI-2753: Add hover effect to request details

[AlyssaWang]

Summary

Change color of code block header on hover in the request details modal.

Testing Guidance

Check that hover effect appears, header should maintain effect while accordion is open.

Q: Should test list items also have this effect?

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 80.24%. Comparing base (2dd6da7) to head (db19605).

Files	Patch %	Lines
...nt/src/components/RequestDetailModal/CodeBlock.tsx	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #495      +/-   ##
==========================================
+ Coverage   80.22%   80.24%   +0.01%     
==========================================
  Files         240      240              
  Lines       11881    11893      +12     
  Branches     1161     1162       +1     
==========================================
+ Hits         9532     9543      +11     
  Misses       1691     1691              
- Partials      658      659       +1     

Flag	Coverage Δ
backend	93.70% <ø> (ø)
frontend	74.22% <93.33%> (+0.02%)	⬆️

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[mrnosal]

Hover effect works as expected - code changes look good.