This should result in some additional cache hits as I personally use
garnix.
Also added `-v` cachix arg to try to figure out why CI jobs aren't
pushing any paths. Right now they just show ["Pushing is
disabled."](https://github.com/zed-industries/zed/actions/runs/15293723678/job/43018512167#step:13:3)
but I'm not sure if that's due to the `pushFilter` or misconfigured
secrets.
Release Notes:
- N/A
Now that the nix build is working again, re-enable nightly builds and
refactor the workflow for re-use between nightly releases and CI jobs.
Release Notes:
- N/A
---------
Co-authored-by: Rahul Butani <rrbutani@users.noreply.github.com>