fix(openai): replace deprecated gpt-4-vision-preview with gpt-4o in TestMultiContentImage

[karsharma10]

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When running multicontent_test.go under llms/openai got error:

API returned unexpected status code: 404: The model gpt-4-vision-preview has been deprecated, learn more here: https://platform.openai.com/docs/deprecations

Follow the deprecations guide link above :

Thus, I changed: gpt-4-vision-preview -> gpt-4o in the multicontent_test.go