unable to query github repos (500)

### Describe the bug

The following prompt fails with 500

```
@github list files from https://github.com/alpinejs/alpine and first 10 lines of readme and index.html
```

I have `lockdown` disabled:

```json
"github.copilot.chat.githubMcpServer.enabled": true,
"github.copilot.chat.githubMcpServer.lockdown": false,
"github.copilot.chat.githubMcpServer.readonly": true,
```

Sometimes it returns an answer, but still doesn't work.

Start by reproducing the reported prompt against the GitHub MCP server with the shown readonly and lockdown settings, then inspect the resulting server error details and request path. Done means the repository listing and first 10 lines of README and index.html complete without a 500 response.

索引モデルが issue の本文から書いたものです。