Add error reporting for the following go-git broken state

[nerdalert]

Error handle the following:

Apr 11 21:00:05 ip-172-31-13-79.us-east-2.compute.internal instruct-lab-bot-worker[181976]: 2024-04-11T21:00:05.278Z        ERROR        cmd/generate.go:455        Could not fetch PR branch: some refs were not updated        {"job": "119", "pr_number": "620", "work_dir": "/home/fedora/instruct-lab-bot", "origin": "origin", "pr_branch_name": "pr-620"}

Apr 11 21:00:05 ip-172-31-13-79.us-east-2.compute.internal instruct-lab-bot-worker[181976]: github.com/instruct-lab/instruct-lab-bot/worker/cmd.(*Worker).processJob

Apr 11 21:00:05 ip-172-31-13-79.us-east-2.compute.internal instruct-lab-bot-worker[181976]:         /home/fedora/instruct-lab-bot/bot-repo/worker/cmd/generate.go:455

[nerdalert]

Resolved by #207