When I click @copilot in a comment on a Pull Request, Copilot works, but it doesn't commit the changes to the PR

### Describe the bug

I use CodeRabbit to review pull requests, and based on a comment made by CodeRabbit or any user, I mention Copilot with @copilot to have it address the comment. It starts a work session, but doesn’t commit anything. The first screenshot shows the start of the session on the Pull Request screen, and the second shows the action that was performed in the Copilot instance that was launched based on my comment.

### Affected version

_No response_

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

Start with the @copilot workflow described in the issue: mention Copilot in a pull request comment and observe the resulting work session and pull request state. Use the attached screenshots as the expected context, then determine why the session does not produce a commit; completion should reproduce the behavior and result in the requested changes being committed to the pull request.

Written by the indexing model from the issue text.