test(react): increase coverage for ComboBox

[adamalston]

No issue.

Increased test coverage for ComboBox.

Changelog

Changed

• Increased test coverage for ComboBox.

Testing / Reviewing

yarn test --coverage \
  --runTestsByPath packages/react/src/components/ComboBox/ComboBox-test.js \
  --collectCoverageFrom=packages/react/src/components/ComboBox/ComboBox.tsx

PR Checklist

As the author of this PR, before marking ready for review, confirm you:

• Reviewed every line of the diff
• Updated documentation and storybook examples
• Wrote passing tests that cover this change
• Addressed any impact on accessibility (a11y)
• Tested for cross-browser consistency
• Validated that this code is ready for review and status checks should pass

More details can be found in the pull request guide

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.84%. Comparing base (69d989e) to head (f2c64a9).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21832      +/-   ##
==========================================
+ Coverage   87.75%   94.84%   +7.08%     
==========================================
  Files         536      537       +1     
  Lines       43637    45108    +1471     
  Branches     6696     7980    +1284     
==========================================
+ Hits        38293    42781    +4488     
+ Misses       5193     2183    -3010     
+ Partials      151      144       -7     

Flag	Coverage Δ
main-packages	87.91% <ø> (-0.04%)	⬇️
web-components	98.28% <ø> (+10.68%)	⬆️

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[adamalston]

I don't plan to mark this pull request as ready for review until some of my earlier pull requests have been reviewed. I want to avoid diverting attention from them. Otherwise, these changes are ready to go.