fix(bootstrap): remove image scanning configuration (#21342)

Remove image scanning configuration for the staging ECR repository.

- Image Scanning Configuration in the bootstrap template causes problems
  in regions where image scanning is not available.
- Scanning configuration at the repository level has been deprecated in
  favor of configuration at the registry level, which also allows more
  configuration (basic vs. enhanced scanning).

Because of a bug in the ECR CloudFormation resource, removing the
configuration value does not actually turn it off. Therefore, for
people who have successfully bootstrapped in the past, the scanning
feature will be left as-is.

----

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

packages/aws-cdk/lib/api/bootstrap/bootstrap-template.yaml

@@ -203,8 +203,6 @@ Resources:
     Type: AWS::ECR::Repository
     Properties:
       ImageTagMutability: IMMUTABLE
-      ImageScanningConfiguration:
-        ScanOnPush: true
       RepositoryName:
         Fn::If:
           - HasCustomContainerAssetsRepositoryName
@@ -510,7 +508,7 @@ Resources:
       Type: String
       Name:
         Fn::Sub: '/cdk-bootstrap/${Qualifier}/version'
-      Value: '13'
+      Value: '14'
 Outputs:
   BucketName:
     Description: The name of the S3 bucket owned by the CDK toolkit stack