Check nix formatting too -- why not?

.forgejo/workflows/build.yaml

@@ -1,5 +1,12 @@
 on: [push]
 jobs:
+  formatting-nix:
+    runs-on: beefcake
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+    - name: alejandra -c .
+      run: 'nix develop -c alejandra -c .'
   build:
     runs-on: beefcake
     steps:
@@ -14,7 +21,7 @@ jobs:
       uses: actions/checkout@v3
     - name: cargo test
       run: 'nix develop -c cargo test'
-  formatting:
+  formatting-rust:
     runs-on: beefcake
     steps:
     - name: Checkout