cleanup: change *kubeclient.Clientset to kubeclient.Interface in unregister module

[wulemao]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

cleanup: change *kubeclient.Clientset to kubeclient.Interface in unregister module

• Improved Abstraction: By using the interface, we enhance the code's flexibility, making it easier to swap out implementations or mock dependencies for testing.
• Easier Testing: Interfaces facilitate unit testing by allowing the use of mock clients, thereby improving test coverage and reliability.
• Code Maintainability: This change promotes better software design principles, making the codebase easier to understand and maintain.

Which issue(s) this PR fixes:

Part of #5380

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[karmada-bot]

Welcome @wulemao! It looks like this is your first PR to karmada-io/karmada 🎉

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.58%. Comparing base (07c6cb4) to head (e0017b6).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5594   +/-   ##
=======================================
  Coverage   41.58%   41.58%           
=======================================
  Files         655      655           
  Lines       55753    55753           
=======================================
  Hits        23186    23186           
  Misses      31062    31062           
  Partials     1505     1505           

Flag	Coverage Δ
unittests	41.58% <ø> (ø)

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[chaosi-zju]

/lgtm

[RainbowMango]

/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: RainbowMango

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• pkg/karmadactl/OWNERS [RainbowMango]

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[chaosi-zju]

/retest