community: Enhance Github error prompt (#15248)
- **Description:** The Github error prompt is confused because of JWT
enctrypt to somebody not familiar with Github connection method. This PR
is to add some useful error prompt to help users troubleshooting.
- **Issue:**
https://github.com/langchain-ai/langchain/issues/14550#issuecomment-1867445049
- **Dependencies:** None,
- **Twitter handle:** None
