tools: do not swallow error in lint-nix workflow

Author: aduh95

.github/workflows/linters.yml

@@ -151,10 +151,13 @@ jobs:
           sparse-checkout-cone-mode: false
       - uses: cachix/install-nix-action@2126ae7fc54c9df00dd18f7f18754393182c73cd  # v31.9.1
       - name: Lint Nix files
+        id: lint-step
         run: |
           nix-shell -I nixpkgs=./tools/nix/pkgs.nix -p 'nixfmt-tree' --run '
             treefmt --quiet --ci
-          ' || git --no-pager diff --exit-code
+          '
+      - run: git --no-pager diff
+        if: ${{ failure() && steps.lint-step.conclusion == 'failure' }}
 
   lint-py:
     if: github.event.pull_request.draft == false