[Feature] add ut for job spec in api server

[Basasuya]

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• [X] I had searched in the issues and found no similar feature requirement.

Description

relate to https://github.com/ray-project/kuberay/pull/416 we have merge the job spec server. But the unit test is relatively lacking

Use case

No response

Related issues

No response

Are you willing to submit a PR?

• [X] Yes I am willing to submit a PR!