Emoji in message causes API failure

[aashishkapur]

        openAIClient := openai.NewClient(openaioption.WithAPIKey(......))

	st := `🏴󠁧󠁢󠁷󠁬󠁳󠁿 Welsh`
	params := &openai.ChatCompletionNewParams{
		Model:    openai.F(openai.ChatModelGPT4o2024_11_20),
		Messages: openai.F([]openai.ChatCompletionMessageParamUnion{openai.SystemMessage(st)}),
	}

	resp, err := openAIClient.Chat.Completions.New(ctx, *params)
	if err != nil {
		log.Fatal(err)
	}

produces

POST "https://api.openai.com/v1/chat/completions": 400 Bad Request {
    "error": {
        "message": "We could not parse the JSON body of your request. (HINT: This likely means you aren't using your HTTP library correctly. The OpenAI API expects a JSON payload, but what was sent was not valid JSON. If you have trouble figuring out how to fix this, please contact us through our help center at help.openai.com.)",
        "type": "invalid_request_error",
        "param": null,
        "code": null
    }
}

The SDK doesn't appear to handle this edge case - it seems to handle other emojis just fine.