ci: deploy upstream on changes

.forgejo/workflows/build.yaml

@@ -0,0 +1,17 @@
+name: Build
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  # deploy it upstream
+  deploy:
+    runs-on: docker
+    steps:
+      - name: "Deploy to Skynet"
+        uses: https://forgejo.skynet.ie/Skynet/actions-deploy-to-skynet@v2
+        with:
+          input: 'simple-nixos-mailserver'
+          token: ${{ secrets.API_TOKEN_FORGEJO }}