fix base_url not work in groq

[simplaj]

Why are these changes needed?

The base_url functionality in Groq was not working correctly in AutoGen version 0.4.1. This PR addresses the issue by fixing the logic for handling the base_url parameter, ensuring it functions as expected.

Related issue number

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[marklysze]

@simplaj, thanks so much for adding support for base_url. I've tested your changes and they look good!

Can I have your Discord ID and email so that we can acknowledge your contribution, and also have you sign CLA properly! I'm msze_ on Discord if you wanted to message me, or you can catch me on the AG2 Discord server.

[simplaj]

Thank you for testing and confirming the changes! I appreciate your acknowledgment and would be happy to provide my Discord ID and email for proper CLA signing. My Discord ID is tianzhihua, and my email is [email protected]. I'll also message you on Discord shortly to stay in touch.

Thanks again for your support!

[marklysze]

Looks good, thanks!

[marklysze]

Passed tests, except OpenAI which can't run as not in repo. Won't affect OpenAI as Groq specific. Merging.