feat: add gitea actions workflow

.gitea/workflows/build.yml

@@ -0,0 +1,13 @@
+name: "Test"
+on:  [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container:
+      image: nixos/nix
+      entrypoint: /usr/bin/env bash
+    steps:
+      - uses: actions/checkout@v3
+      - run: nix-channel --add https://nixos.org/channels/nixos-unstable-small nixpkgs
+      - run: nix-channel --update
+      - run: nix  build