fix nixfmt workflos

.github/workflows/flake-check.yml

@@ -3,12 +3,23 @@ on:
   pull_request:
   push:
 jobs:
-  tests:
+  flake-check:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v30
       with:
-        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+        github_access_token: ${{ secrets.github_token }}
     - run: nix flake check
-    - run: nix fmt
+
+  nixfmt:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v30
+      with:
+        github_access_token: ${{ secrets.github_token }}
+    - name: install nixfmt
+      run: nix-env -f <nixpkgs> -iAP nixfmt-rfc-style
+    - name: check that nix files are formatted correctly
+      run : nixfmt --check