Build image on Forgejo runner

.forgejo/workflows/image.yaml

@@ -0,0 +1,26 @@
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: docker/metadata-action@v3
+        id: metadata
+        with:
+          images: git.hamburg.ccc.de/${{ github.repository }}
+      - uses: docker/login-action@v1
+        with:
+          registry: git.hamburg.ccc.de
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - uses: https://github.com/int128/kaniko-action@v1
+        with:
+          push: true
+          tags: ${{ steps.metadata.outputs.tags }}
+          labels: ${{ steps.metadata.outputs.labels }}
+          cache: true
+          cache-repository: git.hamburg.ccc.de/${{ github.repository }}/cache