Merge pull request NixOS#253 from blitz/ci-fix

Fix Github action by updating install-nix-action

Author: edolstra

Diff for: .github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
-    - uses: cachix/install-nix-action@v9
+    - uses: cachix/install-nix-action@v12
       with: 
         skip_adding_nixpkgs_channel: true
     - run: nix-build release.nix