Build image when pushing to main.

Author: fnando

.github/workflows/docker.yml

@@ -2,6 +2,9 @@
 name: Docker
 
 on:
+  push:
+    branches: [main]
+    paths: [Dockerfile]
   workflow_dispatch:
     inputs:
       ref:
@@ -34,11 +37,18 @@ jobs:
         uses: docker/setup-buildx-action@v4
 
       - name: Log in to Docker Hub
+        if: github.event_name != 'push'
         uses: docker/login-action@v4
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
+      # Build only (no push) to validate the Dockerfile on changes to main.
+      - name: Setup vars (push)
+        if: github.event_name == 'push'
+        run: |
+          echo "STELLAR_CLI_REF=${{ github.sha }}" >> $GITHUB_ENV
+
       # Use the published tag as the ref; set both the versioned and `latest` tags.
       - name: Setup vars (release)
         if: github.event_name == 'release'
@@ -78,6 +88,6 @@ jobs:
         with:
           context: .
           platforms: linux/amd64,linux/arm64
-          push: true
+          push: ${{ github.event_name != 'push' }}
           build-args: STELLAR_CLI_REF=${{ env.STELLAR_CLI_REF }}
           tags: ${{ env.DOCKER_TAGS }}