buildx is needed, actually

.gitea/workflows/harmony_composer.yaml

@@ -1,6 +1,5 @@
 name: Compile and package harmony_composer
 on:
-  pull_request:
   push:
     branches:
       - master
@@ -36,6 +35,9 @@ jobs:
 
       # TODO: build ARM images and MacOS binaries (or other targets) too
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: Build and push
         uses: docker/build-push-action@v6
         with: