fix: overview workflow missing checkout (#246)

.github/workflows/overview.yaml

@@ -8,6 +8,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+      - uses: 'actions/checkout@v4'
       - uses: DeterminateSystems/nix-installer-action@main
       - uses: cachix/cachix-action@v14
         with: { name: 'ngi' }