docs: fix overridden spelling in agent comment

[noooooooookro]

The pipeline node comment uses "overriden", which is a misspelling of "overridden". This updates the comment and wraps the line to keep it within the project formatting limit.

Validation:

• ruff check livekit-agents/livekit/agents/voice/agent.py
• ruff format --check livekit-agents/livekit/agents/voice/agent.py
• git diff --check

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.