(pipelines): UpdatePipeline - SelfMutate action injects stack name instead of the stack id

### What is the problem?

I ran into an issue where the UpdatePipeline - SelfMutate action failed. In my situation the Stack Id is different from the Stack Name. Looking at the generated CodeBuild commands I saw that it injected the stackName instead of the stackId. I believe the CDK cli requires a stack id to select the correct stack.

This line is wrong I think:
See https://github.com/aws/aws-cdk/blob/3382e997067f7e9f98ba98f618402b48bea838b9/packages/%40aws-cdk/pipelines/lib/codepipeline/codepipeline.ts#L619

https://github.com/aws/aws-cdk/blob/3382e997067f7e9f98ba98f618402b48bea838b9/packages/%40aws-cdk/pipelines/lib/codepipeline/codepipeline.ts#L628

### Reproduction Steps

Create a pipeline in a stack where the stack id is different from the stack name.
Change the pipeline so it has to do a self update

### What did you expect to happen?

The pipeline should update after a change

### What actually happened?

The UpdatePipeline - SelfMutate action fails because it cannot find the stack in the assembly

### CDK CLI Version

2.15.0

### Framework Version

_No response_

### Node.js Version

14

### OS

Amazon Linux

### Language

Typescript

### Language Version

_No response_

### Other information

_No response_

Start in packages/@aws-cdk/pipelines/lib/codepipeline/codepipeline.ts at the referenced lines 619 and 628, then reproduce the failure with a pipeline whose stack ID differs from its stack name. Verify the generated CodeBuild commands and confirm that self-mutation succeeds and finds the stack in the assembly.

Written by the indexing model from the issue text.