chore: use public.ecr.aws for all test images (#34831)

### Reason for this change

DockerHub as strict rate limits. Use public.ecr.aws for all test instead.

### Description of how you validated changes

Tests are passing

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: mrgrain

packages/@aws-cdk-testing/framework-integ/test/aws-codepipeline-actions/test/assets/Dockerfile

@@ -1 +1 @@
-FROM node:20-alpine
+FROM public.ecr.aws/docker/library/node:20-alpine

packages/@aws-cdk-testing/framework-integ/test/aws-codepipeline-actions/test/integ.pipeline-ecr-image-scan-action.js.snapshot/asset.27f275db75ac03bdc330dbcf7088081a073cf2e4126ccbf4d9b2726213619891/Dockerfile

@@ -675,7 +675,7 @@
          "ECRRepositoryName": {
           "Fn::Sub": "cdk-hnb659fds-container-assets-${AWS::AccountId}-${AWS::Region}"
          },
-         "ImageTag": "30a26f3582aa60a33d76db3f126e70a08bcfd5d4af185230cbb2a37db272ab4e",
+         "ImageTag": "27f275db75ac03bdc330dbcf7088081a073cf2e4126ccbf4d9b2726213619891",
          "CriticalThreshold": 5,
          "HighThreshold": 5,
          "MediumThreshold": 5,