add nixbased build ci

.gitea/workflows/nix-check.yaml

@@ -0,0 +1,13 @@
+name: Verify build
+run-name: ${{ gitea.actor }} is building
+on: [push]
+
+jobs:
+  verify_build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+        with:
+          nix_path: nixpkgs=channel:nixos-24.11
+          - run: nix-build