CI: add check action

.github/workflows/build.yml

@@ -1,6 +1,7 @@
 name: Build
 
 on:
+  workflow_dispatch:
   workflow_call:
     secrets:
       CACHIX_AUTH_TOKEN:
@@ -19,5 +20,5 @@ jobs:
 
     uses: ./.github/workflows/nix.yml
     with:
-      command: nix build -L .#${{ matrix.package }}
+      command: nix build -L .#${{ matrix.package }} -v
     secrets: inherit

.github/workflows/check.yml

@@ -0,0 +1,20 @@
+name: Checks
+
+on: [push, pull_request, workflow_dispatch]
+
+jobs:
+  check:
+    strategy:
+      matrix:
+        command:
+          - NIXPKGS_ALLOW_INSECURE=1 nix flake check --accept-flake-config --impure
+          - nix run nixpkgs#alejandra -- -c . -e ./npins
+
+    uses: ./.github/workflows/nix.yml
+    with:
+      command: ${{ matrix.command }}
+
+  build:
+    needs: check
+    uses: ./.github/workflows/build.yml
+    secrets: inherit