try building

.gitea/workflows/build.yml

@@ -0,0 +1,17 @@
+name: Build image
+run-name: ${{ gitea.actor }} is building an image
+on: [push]
+
+jobs:
+  runs-on: alpine
+  steps:
+    - uses: https://github.com/actions/checkout@v4
+    - name: Set up Docker Buildx
+        uses: https://github.com/docker/setup-buildx-action@v3            
+    - name: Build and push Docker image
+      uses: https://github.com/docker/build-push-action@v5
+      with:
+        context: .
+        file: ./Dockerfile
+        push: true
+        tags: "hal.mafoo.org.uk/mafoo.org.uk/mythic-dns:${{gitea.sha}},hal.mafoo.org.uk/mafoo.org.uk/mythic-dns:latest"