fix(codecov): improve core code coverage

[stephenLYZ]

SUMMARY

This PR supplements the code coverage of the core package to 100%.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #20274 (24ba8a8) into master (41f33a3) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #20274   +/-   ##
=======================================
  Coverage   66.64%   66.65%           
=======================================
  Files        1729     1729           
  Lines       64904    64904           
  Branches     6842     6842           
=======================================
+ Hits        43257    43262    +5     
+ Misses      19897    19893    -4     
+ Partials     1750     1749    -1     

Flag	Coverage Δ
javascript	51.57% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...set-ui-core/src/color/SharedLabelColorSingleton.ts	100.00% <0.00%> (+13.51%)	⬆️

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[zhaoyongjie]

LGTM