ci: minor fix to treefmt check

.github/workflows/treefmt.yml

@@ -8,18 +8,20 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: cachix/install-nix-action@v22
-    - uses: actions/checkout@v3
-    - id: files
+    - uses: actions/checkout@v4
+    - id: changed-files
       uses: tj-actions/changed-files@v44
     - name: Run treefmt
       run: nix fmt
     - name: Check diff
+      env:
+        ALL_CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
       run: |
         unformatted_touched=()
         unformatted_untouched=()
         while IFS= read -r unformatted_file; do
           matched=
-          for changed_file in ${{ steps.files.outputs.all }}; do
+          for changed_file in ${ALL_CHANGED_FILES}; do
             if [[ "$changed_file" == "$unformatted_file" ]]; then
               unformatted_touched+=("$unformatted_file")
               matched=1
@@ -36,6 +38,8 @@ jobs:
           printf '%s\n' "${unformatted_untouched[@]}"
         fi
 
+        echo # blank line
+
         if (( ${#unformatted_touched[@]} )); then
           echo "These files are created/edited but not formatted:"
           printf '%s\n' "${unformatted_touched[@]}"