add forgejo workflow

.forgejo/workflows/build.yaml

@@ -0,0 +1,17 @@
+name: build nixos-runner
+on:
+  - push
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    container: docker.io/jcollie/nixos-runner:latest
+    steps:
+      - uses: actions/checkout@v4
+      - run: set
+      - run: nix build -L .#nixos-runner
+      - run: nix run .#push-container -- result
+        env:
+          REGISTRY: https://git.ocjtech.us/${{ github.repository_owner }}
+          REPOSITORY: nixos-runner
+          USERNAME: ${{ github.actor }}
+          PASSWORD: ${{ github.token }}