chore: fix broken link to cloud assembly schema (#29773)

### Issue # (if applicable)

### Reason for this change

The link to the `cloud-assembly-schema` in the [design/cloud-assembly.md](https://github.com/aws/aws-cdk/blob/main/design/cloud-assembly.md) is broken.

![page-1](https://github.com/aws/aws-cdk/assets/24818752/20e66831-bf5c-47c4-90d1-485c3ba0da39)

![page-2](https://github.com/aws/aws-cdk/assets/24818752/0ccee86e-58ff-49b2-9997-cc55ab022605)

### Description of changes

Changed the link to correct link.

### Description of how you validated changes

### 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*

design/cloud-assembly.md

@@ -1,3 +1,3 @@
 # Cloud Assembly Specification, Version 2.0
 
-See [cloud-assembly-schema](../packages/@aws-cdk/cloud-assembly-schema/README.md)
+See [cloud-assembly-schema](../packages/aws-cdk-lib/cloud-assembly-schema/README.md)