CI: Replace Garnix with GHA

Sorry Garnix!

Author: 9999years

.github/workflows/ci.yaml

@@ -0,0 +1,39 @@
+---
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  ci:
+    name: nix flake check (${{ matrix.platform.runner }})
+    runs-on: ${{ matrix.platform.runner }}
+    timeout-minutes: 60
+    strategy:
+      fail-fast: false
+      matrix:
+        platform:
+          - runner: ubuntu-latest
+            system: x86_64-linux
+          - runner: macos-latest
+            system: aarch64-darwin
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+
+      - uses: cachix/install-nix-action@7be5dee1421f63d07e71ce6e0a9f8a4b07c2a487 # v31.6.1
+        with:
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+          extra_nix_config: |
+            extra-experimental-features = nix-command flakes
+            accept-flake-config = true
+
+      - name: nix flake check
+        run: nix flake check --print-build-logs

flake.nix

@@ -21,12 +21,6 @@
     };
   };
 
-  nixConfig = {
-    extra-substituters = ["https://cache.garnix.io"];
-    extra-trusted-substituters = ["https://cache.garnix.io"];
-    extra-trusted-public-keys = ["cache.garnix.io:CTFPyKSLcx5RMJKfLo5EEPUObbA78b0YQ2DTCJXqr9g="];
-  };
-
   outputs = inputs @ {
     self,
     nixpkgs,