fix: make sure maintenance=true is honored properly

[harshavardhana]

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

fix: make sure maintenance=true is honored properly

Motivation and Context

fixes a regression from #18700

How to test this PR?

minio server ~/test
curl http://localhost:9000/minio/health/cluster?maintenance=true (this must fail)

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 from prom: Add online and healing drives metrics per erasure set #18700
• Unit tests added/updated
• Internal documentation updated
• Create a documentation update request here

[vadmeste]

LGTM