Use latest madmin-go for policy content check

[shtripat]

Community Contribution License

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under the terms of the Apache 2 license.
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contributions to the project maintainers under the Apache 2 license.

Description

Motivation and Context

Fixes: #5108

How to test this PR?

Run command mc admin policy create ALIAS cust-pol pol.json with empty pol.json and it should error

mc: <ERROR> Unable to create new policy: policy input cannot be empty.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Optimization (provides speedup with no functional changes)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• Fixes a regression (If yes, please add commit-id or PR # here)
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here