Added tests for examples/customresourceinterpreter/webhook

[anujagrawal699]

Description:
This pr introduces tests for karmada/examples/customresourceinterpreter/webhook/app/workloadwebhook.go and webhook.go.

Additions:

1. workloadwebhook_test.go
2. webhook_test.go

What type of PR is this?
/kind failing-test
/kind feature

What this PR does / why we need it:
This PR adds comprehensive tests for testing core functionality of customresourceinterpreter/webhook.

Which issue(s) this PR fixes:
Fixes a part of #5236

Does this PR introduce a user-facing change?:

NONE

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 31.18%. Comparing base (80037ce) to head (a049bf4).
Report is 139 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5433      +/-   ##
==========================================
+ Coverage   30.94%   31.18%   +0.23%     
==========================================
  Files         638      639       +1     
  Lines       44307    44313       +6     
==========================================
+ Hits        13712    13818     +106     
+ Misses      29604    29498     -106     
- Partials      991      997       +6     

Flag	Coverage Δ
unittests	31.18% <ø> (+0.23%)	⬆️

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[anujagrawal699]

@XiShanYongYe-Chang Please take a look.

[XiShanYongYe-Chang]

Thanks @anujagrawal699
/assign

[XiShanYongYe-Chang]

/lgtm
/approve

[XiShanYongYe-Chang]

In my opinion, this test function may not actually be able to take care of the code quality.
To be honest, I don't know how to test the corresponding function. Let's accept it for now and replace it later if there is a better way to test it.

[anujagrawal699]

Yeah, some functions are harder to test in this file. That's the reason i skipped some of them.

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: XiShanYongYe-Chang

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