cachix action failing for unknown reasons, patch to use local runner

.github/workflows/nix.yml

@@ -18,10 +18,10 @@ jobs:
           - nixos-unstable
           - nixos-22.11
           - nixos-23.05
-    runs-on: ubuntu-latest
+    runs-on: native
+    container: pjjw/nix-flake-runner:1
     steps:
       - uses: actions/checkout@v3
-      - uses: cachix/install-nix-action@v22
       - run: nix-shell --run ./ci.sh
         env:
           CI_REGISTRY_AUTH: '${{ secrets.REGISTRY_AUTH }}'