Copilot Insiders cannot create PRs

### Describe the bug

Copilot reports that the MCP server does not expose a pull-request creation tool. PR read operations work.
### Affected version

1.12 remote server

### Steps to reproduce the behavior

1. Install the MCP server in VSCode

"github": {
"type": "http",
"url": "https://api.githubcopilot.com/mcp"
}

Ask AI in chat to create a PR - reports the error shown above.
AI can create the PR with gh cli

### Expected vs actual behavior

Expect AI to be able to use MCP server to create PRs.
NB - issue creation works

### Logs

Start with the remote 1.12 MCP server endpoint and inspect the exposed tool list, comparing it with the working issue-creation operation. Reproduce the VSCode Copilot request for pull-request creation and verify that the server exposes the operation and can complete the request successfully.

由索引模型根据 Issue 内容生成。