chore(docs): fix warning format in metrics documentation

[leandrodamascena]

Description of your changes

The rendering of this banner is wrong as the line below is missing a tab.

BEFORE

AFTER

How to verify this change

Related issues, RFCs

Issue number: #1422

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding changes to the examples
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published
• The PR title follows the conventional commit semantics

Breaking change checklist

Is it a breaking change?: NO

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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[dreamorosi]

Thank you for spotting this & submitting a fix, appreciate it!