Change Amcrest example to subtype=3

[PrplHaz4]

I think this was meant to be a 3.

Proposed change

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code
• [ X ] Documentation Update

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Add dahua and amcrest to camera specific documentation #15605

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• The code has been formatted using Ruff (ruff format frigate)

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