ci(test): add job for flake checks

.github/workflows/test.yml

@@ -0,0 +1,17 @@
+name: test
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  checks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v24
+      - name: flake check
+        run: nix flake check