Correct span_kind casing.

[nathanhammond]

This casing does not agree with the OpenInference spec, or the enum from Python.

References:

https://github.com/Arize-ai/openinference/blob/main/spec/semantic_conventions.md?plain=1#L43

https://github.com/Arize-ai/openinference/blob/main/python/openinference-semantic-conventions/src/openinference/semconv/trace/init.py#L233-L241

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[RogerHYang]

@nathanhammond Thanks for the PR. Can you please sign the CLA by following the instructions from the CLA Assistant above?

[nathanhammond]

Not a copyrightable change (below the threshold of originality as a mechanical change) but if necessary you are encouraged to recreate this.