[MINOR] Make spark context transient to avoid serialization

[boneanxs]

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[boneanxs]

@hudi-bot run azure

[hudi-bot]

CI report:

• d0d9911 Azure: FAILURE Azure: SUCCESS

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• @hudi-bot run azure re-run the last Azure build

[boneanxs]

Hi @leesf @wangxianghu, could you pls review this?

[xushiyan]

@boneanxs HoodieEngineContext itself is not serializable. In HoodieTable we also mark HoodieEngineContext transient. So I don't think the change is needed. Can you confirm please?

[boneanxs]

Thanks for clearing me, I may run into the wrong code path when fixing one issue, I'll close this.