build: Try building docker container on pull requests

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

.github/workflows/docker-image.yaml

@@ -4,6 +4,8 @@ on:
   push:
     branches: main
     paths: resources/Dockerfile
+  pull_request:
+    paths: resources/Dockerfile
 
 jobs:
   main:
@@ -19,12 +21,14 @@ jobs:
         uses: docker/setup-buildx-action@v1
 
       - name: Login to DockerHub
+        if: ${{ github.event_name == 'push' }}
         uses: docker/login-action@v1 
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       - name: Build and push
+        if: ${{ github.event_name == 'push' }}
         uses: docker/build-push-action@v2
         with:
           file: ./resources/Dockerfile
@@ -32,5 +36,13 @@ jobs:
           push: true
           tags: cloudhypervisor/dev:latest
 
+      - name: Build only
+        if: ${{ github.event_name == 'pull_request' }}
+        uses: docker/build-push-action@v2
+        with:
+          file: ./resources/Dockerfile
+          platforms: linux/amd64,linux/arm64
+          tags: cloudhypervisor/dev:latest
+
       - name: Image digest
         run: echo ${{ steps.docker_build.outputs.digest }}