Global zizmor workflow runs even if no relevant changes exist in PR

The org wide zizmor workflow can be optimized to avoid running when it shouldn't. There are some checks in place already to do this but they seem to not work properly.

Example run https://github.com/grafana/levitate-grafana-ci/actions/runs/15211516945
There is no need to run at least the last step (generate and upload) as there is nothing zizmor relevant that was changed.