chore(ci): add nix flake check

.github/workflows/ci.yml

@@ -61,6 +61,25 @@ jobs:
         cargo +nightly update -Z minimal-versions
         git diff --exit-code Cargo-minimal.lock
 
+  nix-flake-check:
+    name: Check Nix flake
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Install Nix
+      uses: cachix/install-nix-action@v31
+
+    - name: Check flake
+      run: nix flake check
+
+    - name: Set Cargo.lock
+      run: cp Cargo-minimal.lock Cargo.lock
+
+    - name: Build with default dev shell
+      run: nix develop --command cargo build --all-features --locked
+
   build:
     name: Build and Test
     runs-on: ubuntu-latest