Fix 0.2 Quickstart example llm_config issue

[victordibia]

Why are these changes needed?

Fix 0.2 Quickstart example llm_config issue

Related issue number

#2038 , (see comment)

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/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.