fix wrong number in doc

[charles-lei]

Description

Fix wrong number in adv_agents.md

Where has this been tested?

• Platform(s): ...
• Python version(s): ...
• Unreal Engine version(s): ...

Possible Drawbacks

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This change is 

[update-docs[bot]]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update our CHANGELOG.md based on your changes.