more tweaks

.github/workflows/quality.yaml

@@ -14,6 +14,7 @@ jobs:
       lua: ${{ steps.changes.outputs.lua }}
       markdown: ${{ steps.changes.outputs.markdown }}
       vimdoc: ${{ steps.changes.outputs.vimdoc }}
+      nix: ${{ steps.changes.outputs.nix }}
     steps:
       - uses: actions/checkout@v4
       - uses: dorny/paths-filter@v3
@@ -31,6 +32,9 @@ jobs:
               - '*.md'
             vimdoc:
               - 'doc/**'
+            nix:
+              - '*.nix'
+              - 'flake.lock'
 
   lua-format:
     name: Lua Format Check
@@ -76,6 +80,16 @@ jobs:
       - uses: cachix/install-nix-action@v31
       - run: nix develop .#ci --command vimdoc-language-server check doc/
 
+  nix-format:
+    name: Nix Format Check
+    runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.nix == 'true' }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v31
+      - run: nix fmt -- --check .
+
   markdown-format:
     name: Markdown Format Check
     runs-on: ubuntu-latest