update github action to v4

Author: piotrkwiecinski

.github/workflows/update-snapshot.yml

@@ -9,7 +9,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         ssh-key: ${{ secrets.SSH_PRIVATE_KEY }}
     - uses: cachix/install-nix-action@v21