Fix the failed image build workflow (knative#6052)

* fix: simplify the watched directory by watching the whole bookstore dir

* fix: We are only providing the builds for linux platform

Author: Leo6Leo

Diff for: .github/workflows/knative-docs-image.yaml

@@ -5,8 +5,7 @@ on:
     branches: ['main']
     paths:
     - "code-samples/serving/hello-world/helloworld-go/**"
-    - "code-samples/eventing/bookstore-sample-app/solution/frontend/**"
-    - "code-samples/eventing/bookstore-sample-app/solution/node-server/**"
+    - "code-samples/eventing/bookstore-sample-app/**"
     - "docs/serving/autoscaling/autoscale-go/**"
     - "hack/docker/**"
     - ".github/workflows/knative-docs-image.yaml"
@@ -60,14 +59,14 @@ jobs:
         uses: docker/build-push-action@v4
         with:
           push: true
-          platforms: linux/amd64,linux/arm64,linux/ppc64le,linux/s390x, windows/amd64, windows/arm64, darwin/amd64, darwin/arm64
+          platforms: linux/amd64,linux/arm64
           context: ./code-samples/eventing/bookstore-sample-app/solution/frontend
           tags: ghcr.io/knative/bookstore-frontend:latest
 
       - name: Build sample-app's node-server image
         uses: docker/build-push-action@v4
         with:
           push: true
-          platforms: linux/amd64,linux/arm64,linux/ppc64le,linux/s390x, windows/amd64, windows/arm64, darwin/amd64, darwin/arm64
+          platforms: linux/amd64,linux/arm64
           context: ./code-samples/eventing/bookstore-sample-app/solution/node-server
           tags: ghcr.io/knative/node-server:latest