use Nix environment in CI

Author: Twey

.github/workflows/main.yml

@@ -15,16 +15,8 @@ jobs:
   backend:
     runs-on: ubuntu-latest
     steps:
-      - name: 'Checkout'
-        uses: actions/checkout@v3
-
-      - name: 'Install Rust toolchain'
-        uses: actions-rust-lang/setup-rust-toolchain@v1
-
-      - name: 'Install Protoc'
-        uses: arduino/setup-protoc@v3
-        with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
+      - uses: actions/checkout@v3
+      - uses: nicknovitski/nix-develop@v1
 
       - name: 'Install linera-storage-service'
         uses: taiki-e/cache-cargo-install-action@v2