Fatal error when running `glab mr checkout` when mr is already checked out

Checklist

• I'm using the latest version of the extension (Run glab --version)
  • Extension version: glab version 1.24.1-62-gd740b39 (2023-01-25)
• Operating System and version: OS X

Summary

After a checking out an MR, the MR's branch may get updated and a user may need to update the branch again.

Running glab mr checkout <id> again will cause a fatal error and the branch will not be updated.

Steps to reproduce

1. glab mr checkout 46
2. (optional - occurs if you so this step or not) add a commit to the MR's branch
3. Once mr branch is checkout out, run it again: glab mr checkout 46

What is the current bug behavior?

❯ glab mr checkout 46 fatal: refusing to fetch into branch 'refs/heads/1-issue-12' checked out at '/Users/jmccure/code/test2target' exit status 128

What is the expected correct behavior?

If no changes - "branch is up to date message"

If there are changes - some indication that changes have been pulled

Relevant logs and/or screenshots