Copilot CLI on WSL must use git-credential-manager to securely store tokens.

### Describe the feature or problem you'd like to solve

Currently, when I log into the GitHub Copilot CLI on WSL, I see the below warning(?).

Note that I already have git configured to use git-credential-manager for logins ([details](https://learn.microsoft.com/en-us/windows/wsl/tutorials/wsl-git#git-credential-manager-setup)).

Can the Copilot CLI also piggyback on this mechanism?

### Proposed solution

_No response_

### Example prompts or workflows

_No response_

### Additional context

_No response_

Start by reproducing the Copilot CLI login warning on WSL and tracing its existing token-storage path alongside the linked Git Credential Manager setup. Done means the CLI uses the configured credential mechanism for login tokens and the warning no longer appears; verify both authentication and subsequent CLI use.

Written by the indexing model from the issue text.