Added second part of unit tests for pkg/scheduler

[anujagrawal699]

Description:
This PR significantly enhances the unit tests for the scheduler package and is the second part of unit tests for it. The improvements aim to increase code reliability, maintainability, and test coverage for various scheduler functions.

Note:
The CI tests might fail because the imports needed for tests are included in the first part of unit tests for scheduler module.

Modifications:
pkg/scheduler/scheduler_test.go

Key Improvements:

1. Added tests for scheduleClusterResourceBindingWithClusterAffinity and scheduleClusterResourceBindingWithClusterAffinities.
2. Added tests for the worker functionality and scheduleNext method.
3. Added tests for the placementChanged function.
4. Added new test cases for the TestCreateScheduler

Test Coverage:
pkg/scheduler/scheduler_test.go: 29.71% to 66.90%

What type of PR is this?
/kind feature

Which issue(s) this PR fixes:
Fixes a part of #5470

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 38.63%. Comparing base (bf771c7) to head (261cbdb).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5681      +/-   ##
==========================================
+ Coverage   38.50%   38.63%   +0.13%     
==========================================
  Files         649      649              
  Lines       45133    45133              
==========================================
+ Hits        17378    17438      +60     
+ Misses      26421    26363      -58     
+ Partials     1334     1332       -2     

Flag	Coverage Δ
unittests	38.63% <ø> (+0.13%)	⬆️

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[anujagrawal699]

@XiShanYongYe-Chang Please take a look.

[XiShanYongYe-Chang]

/assign

[XiShanYongYe-Chang]

/lgtm
/approve

[karmada-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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