[CI] fix cachix install-nix

There appears to be some unknowns regarding ensuring nix is installed,
but not overwritten (see
cachix/install-nix-action#98 and
https://github.com/cachix/install-nix-actions/pull/100/files).

.github/workflows/ci.yaml

@@ -28,8 +28,15 @@ jobs:
       with:
         submodules: true
 
+    - name: Probe Build Environment
+      run: |
+        id
+        uname -a
+        pwd
+        cat /etc/os-release
+      
     - name: Install Nix
-      uses: cachix/install-nix-action@v16
+      uses: cachix/install-nix-action@v14.1
       with:
         nix_path: nixpkgs=channel:nixos-21.11
         install_url: https://releases.nixos.org/nix/nix-2.4/install