tests(ci): run flake checks in github actions

.github/workflows/nix-github-actions.yml

@@ -0,0 +1,33 @@
+name: Nix Flake actions
+
+on:
+  push:
+    branches: [ "main", "next-major" ]
+  pull_request:
+    branches: [ "main", "next-major" ]
+
+jobs:
+  nix-matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+      - id: set-matrix
+        name: Generate Nix Matrix
+        run: |
+          set -Eeu
+          matrix="$(nix eval --json '.#githubActions.matrix')"
+          echo "matrix=$matrix" >> "$GITHUB_OUTPUT"
+
+  nix-build:
+    name: ${{ matrix.name }} (${{ matrix.system }})
+    needs: nix-matrix
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix: ${{fromJSON(needs.nix-matrix.outputs.matrix)}}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+      - run: nix build -L '.#${{ matrix.attr }}'

flake.nix

@@ -3,7 +3,7 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.11";
-    systems.url = "github:nix-systems/default-linux";
+    systems.url = "github:nix-systems/default";
 
     rust-overlay.url = "github:oxalica/rust-overlay";
     rust-overlay.inputs.nixpkgs.follows = "nixpkgs";
@@ -13,6 +13,9 @@
 
     git-hooks.url = "github:chrjabs/git-hooks.nix";
     git-hooks.inputs.nixpkgs.follows = "nixpkgs";
+
+    nix-github-actions.url = "github:nix-community/nix-github-actions";
+    nix-github-actions.inputs.nixpkgs.follows = "nixpkgs";
   };
 
   outputs = {
@@ -22,6 +25,7 @@
     rust-overlay,
     nix-tools,
     git-hooks,
+    nix-github-actions,
   }: let
     lib = nixpkgs.lib;
     forAllSystems = lib.genAttrs (import systems);
@@ -164,5 +168,9 @@
           };
         };
     });
+
+    githubActions = nix-github-actions.lib.mkGithubMatrix {
+      checks = self.checks // self.packages;
+    };
   };
 }