docs: unify get weather function name in openai-harmony for consistency

[kibitzing]

Summary

This pull request corrects an error in the tool-calling example where the function names used for invocation did not match the actual function name defined in the tools section.

The tool was defined with the name get_current_weather. However, the example code that demonstrated its usage was incorrectly using get_weather and lookup_weather, creating a discrepancy.

This commit fixes the example code to consistently use the function name, get_current_weather, throughout the entire request-response flow, aligning it with the existing tool definition.

Motivation

The primary motivation for this change is to prevent confusion for anyone reading the code.
By this fix, a developer following this code will see a clear and logical flow, free from the ambiguity caused by mismatched names, making the learning process much smoother.

[kibitzing]

Hello @dkundel-openai,
Thanks for the review and approval, if there is anything I need to do, please let me know!