smaple yaml code for prevent_merge

.github/workflows/phase3/prevent_merge.yaml

@@ -0,0 +1,42 @@
+name: Build Container Image
+
+on:
+  push:
+    branches:
+      - main
+      - master
+    # Check if the commit message contains 'BUILD_CONTAINER_IMAGE'
+    paths-ignore:
+      - '.github/workflows/**'
+  pull_request:
+    branches:
+      - main
+      - master
+
+jobs:
+  build:
+    if: |
+      github.event_name == 'push' &&
+      (github.event.head_commit.message contains 'BUILD_CONTAINER_IMAGE' || github.ref == 'refs/heads/main' || github.ref == 'refs/heads/master') ||
+      github.event_name == 'pull_request' && github.event.action == 'closed' && github.event.pull_request.merged == true
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_ACCESS_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: <your-dockerhub-username>/guestbook-go:latest