add an E2E test for dependency aggregation

[Kexin2000]

What type of PR is this?

/kind feature
/kind testing

What this PR does / why we need it:
It introduces a new E2E test to ensure that shared dependencies produce a single attached ResourceBinding with accurate RequiredBy tracking.

Which issue(s) this PR fixes:
Fixes # 6000

Special notes for your reviewer:

• Added a new E2E test in test/e2e/suites/base/dependency_aggregation_test.go to verify multi dependency tracking behavior.
• The test ensures:
  • Two deployments referencing the same ConfigMap produce a single attached ResourceBinding.
  • The RequiredBy field in the attached ResourceBinding includes both parents.
  • Updates to RequiredBy occur when one parent stops referencing the shared dependency.

Does this PR introduce a user-facing change?:
None

[karmada-bot]

@Kexin2000: The label(s) kind/testing cannot be applied, because the repository doesn't have them.

In response to this:

What type of PR is this?

/kind feature
/kind testing

What this PR does / why we need it:
It introduces a new E2E test to ensure that shared dependencies produce a single attached ResourceBinding with accurate RequiredBy tracking.

Which issue(s) this PR fixes:
Fixes # 6000

Special notes for your reviewer:

• Added a new E2E test in test/e2e/suites/base/dependency_aggregation_test.go to verify multi dependency tracking behavior.
• The test ensures:
• Two deployments referencing the same ConfigMap produce a single attached ResourceBinding.
• The RequiredBy field in the attached ResourceBinding includes both parents.
• Updates to RequiredBy occur when one parent stops referencing the shared dependency.

Does this PR introduce a user-facing change?:
None

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[karmada-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.83%. Comparing base (768f929) to head (e99c7d4).
⚠️ Report is 10 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6809      +/-   ##
==========================================
+ Coverage   45.75%   45.83%   +0.08%     
==========================================
  Files         689      690       +1     
  Lines       57176    57300     +124     
==========================================
+ Hits        26159    26266     +107     
- Misses      29390    29403      +13     
- Partials     1627     1631       +4     

Flag	Coverage Δ
unittests	45.83% <ø> (+0.08%)	⬆️

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