Migrate CI to Forgejo Actions

.forgejo/workflows/build_image.yaml

@@ -0,0 +1,18 @@
+on: [push]
+jobs:
+  build_image:
+    runs-on: docker
+    steps:
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to Docker registry (Forgejo)
+        uses: docker/login-action@v3
+        with:
+          registry: git.korhonen.cc
+          username: ${{ secrets.REGISTRY_USER }}
+          password: ${{ secrets.REGISTRY_PASSWORD }}
+      - name: Build and push image
+        uses: docker/build-push-action@v5
+        with:
+          push: true
+          tags: git.korhonen.cc/functionalhacker/hugo-asciidoc-docker-ci:latest