👷 Simplify deadnix workflow

.github/workflows/deadnix.yml

@@ -1,6 +1,7 @@
 name: "Nix: check for unused code"
 
 on:
+  workflow_dispatch:
   pull_request:
   push:
     paths:
@@ -12,17 +13,9 @@ jobs:
     name: Run deadnix
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          ref: ${{ github.ref_name }}
-          persist-credentials: false
+      - uses: actions/checkout@main
       
       - name: Install lix
         uses: ./.github/actions/install-lix
 
-      - uses: cachix/cachix-action@v14
-        with:
-          name: deadnix
-
       - uses: phucleeuwu/deadnix-action@v1