feat(ci): add task to check formatting before building

.github/workflows/build.yml

@@ -1,19 +1,42 @@
 name: Build
-
 on:
   push:
     branches: [ main ]
   pull_request:
     branches: [ main ]
 
 jobs:
+  matrix-setup:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - id: set-matrix
+        run: |
+          echo "matrix=$(jq -c . << EOF
+          {
+            "os": ["ubuntu-latest", "macos-latest"]
+          }
+          EOF)" >> $GITHUB_OUTPUT
+
+  check:
+    needs: matrix-setup
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix: ${{fromJson(needs.matrix-setup.outputs.matrix)}}
+    steps:
+    - uses: actions/checkout@v3
+    - uses: DeterminateSystems/nix-installer-action@main
+    - uses: DeterminateSystems/magic-nix-cache-action@main
+    - run: nix flake check
+
   build:
+    needs: [matrix-setup, check]
     runs-on: ${{ matrix.os }}
     strategy:
-      matrix:
-        os: [ubuntu-latest, macos-latest]
+      matrix: ${{fromJson(needs.matrix-setup.outputs.matrix)}}
     steps:
     - uses: actions/checkout@v3
     - uses: DeterminateSystems/nix-installer-action@main
     - uses: DeterminateSystems/magic-nix-cache-action@main
-    - run: nix build .#mugraph-node
+    - run: nix build .#mugraph-node