Enforce Selection of a Valid GPT Model Before Processing Pull Requests

# Issue Description:
Currently, our system does not mandate the selection of a valid GPT model before processing pull requests, which can lead to inconsistent results or errors. To enhance the robustness and reliability of our processing pipeline, we should implement a requirement that a valid GPT model must be selected before any pull request is processed.

# Proposed Solution:

Introduce a validation step in our pull request processing workflow that checks for the selection of a valid GPT model. If no model is selected, or an invalid option is chosen, the system should prevent the processing of the pull request and prompt the user to select a valid model.

# Expected Benefits:

Ensures consistency and accuracy in processing results.
Prevents errors related to missing or invalid model selections.
Enhances user experience by guiding them to make necessary selections before processing.

# Request for Action:

We need to update the workflow logic to include this validation check and modify the user interface to clearly indicate the requirement of selecting a valid GPT model. I suggest we prioritize this issue in our upcoming development cycle.

# Feedback and Contributions:

Any suggestions or contributions towards implementing this feature are welcome. Please share your thoughts or submit a pull request with proposed changes.