Rollback with a branch references the head of branch, not the SHA

**Describe the bug**
When I roll back with a branch, the deployment references the head of the branch, not the SHA, which can compound the problem. I think this [code](https://github.com/gitploy-io/gitploy/blob/main/internal/server/api/v1/repos/deployment_rollback.go#L61), copying from the `ref` of the initial deployment, makes the bug.