fix(test): JSON snapshot tests for miner params

[akaladarshi]

Part of #6365

Summary of changes

Changes introduced in this pull request:

• Add snapshot tests in the miner_params.rs to increase code coverage

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

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• src/lotus_json/actors/params/miner_params.rs

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