Success reported on failed backport

[s0undt3ch]

This backport run fails due to merge conflicts, however, the action does not report the error.

https://github.com/saltstack/salt/actions/runs/6289260964/job/17075576644#step:3:460

Right now, we don't know how many backport runs actually failed when they reported success.

[s0undt3ch]

Another example https://github.com/saltstack/salt/actions/runs/6088980910/job/16520779280#step:2:146