Add kube-scheduler podgroup unit tests

[shadowinlife]

Purpose of this PR

Proposed changes:

Add kube-scheduler podgroup unit tests to enhanced unit test. Details:

• cover scheduler factory, scheduling, and cleanup code paths with the fake client
• ensure PodGroup sync reuses the existing resourceVersion before issuing Update

After patch:

ok      github.com/kubeflow/spark-operator/v2/internal/scheduler/kubescheduler  3.039s  coverage: 86.5% of statements

I'd like to gradually contribute code to the current open-source project to improve test coverage, so that it can meet our internal usage standards

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

[shadowinlife]

@ChenYi015 this PR is ready for review. thanks

[ChenYi015]

@shadowinlife Thanks for adding unit tests on kube-scheduler integration!
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

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