ci: don't use latest nix

.github/workflows/ci-nix.yml

@@ -7,8 +7,7 @@ jobs:
     name: Rust project
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - name: Install Nix
-      uses: DeterminateSystems/nix-installer-action@main
-    - run: nix develop -c rustc --version
-    - run: nix run
+      - uses: actions/checkout@v3
+      - uses: cachix/install-nix-action@v22
+      - run: nix develop -c rustc --version
+      - run: nix run