Run flake checks on CI

Now all linting, compiling, and testing will be done on CI.

.github/workflows/nix.yaml

@@ -2,24 +2,18 @@ name: "Nix"
 on:
   pull_request:
   push:
+# cancel previous runs when pushing new changes
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
 jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2.3.1
-    - name: Local cache
-      uses: actions/cache@v2
-      with:
-        path: /nix/store
-        key: "${{ runner.os }}-nix-cache"
-    - uses: cachix/install-nix-action@v12
-      with:
-        nix_path: nixpkgs=channel:nixos-unstable
-    # - uses: cachix/cachix-action@v6
-    #   with:
-    #     name: jappie
-    #     signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
-    #     # Only needed for private caches
-    #     #authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-    # - run: nix-build .
-    # - run: nix-shell --run "cd incoming; make all"
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v25
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+          extra_nix_config: "system-features = kvm nixos-test"
+
+      - run: nix flake check -L