fix: python deserialization

[jaluma]

What does this PR do?

This PR is intended to solve a deserialisation problem occurred with the latest version when no function tools are available, crashing when validating pydantic.

Relevant information

• Setup:
  • Mode: Docker container
  • Image: ghcr.io/huggingface/text-generation-inference:2.1.0
  • Model: TinyLlama/TinyLlama-1.1B-Chat-v1.0
  • Python client version: text-generation==0.7.0
• Crash stacktrace:

pydantic_core._pydantic_core.ValidationError: 1 validation error for ChatCompletionChunk
choices.0.delta.tool_calls
  Field required [type=missing, input_value={'role': 'assistant', 'content': 'S'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.5/v/missing

Fixes # (issue)

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• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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[Narsil]

LGTM.

Thanks.