chore: codecov includes files outside of configured packages (#32748)

The [addition](#32641) of `aws-cdk-lib/core` caused other files from `aws-cdk-lib` to be included in the [report](https://app.codecov.io/github/aws/aws-cdk/tree/main/packages%2Faws-cdk-lib). 

![image](https://github.com/user-attachments/assets/5584f55f-9dcd-4afe-829a-ce39cc140e43)

The undesired included files are those that are imported by `aws-cdk-lib/core` unit tests. And since they are in the same package, they are included in the jest report. We could exclude them from jest, but that would mean changing the coverage settings for the entire `aws-cdk-lib` package. Instead, we can ask codecov to ignore them. Compare the previous report with this [one](https://app.codecov.io/github/iliapolo/aws-cdk/commit/8263d053b52ca94db42fa9d04c2481dfac5d54ee/tree/packages/aws-cdk-lib), from my fork, that tests the new configuration.

![image](https://github.com/user-attachments/assets/63f24fa5-9e8f-439a-8b19-f876a171e5a9)

codecov.yml

@@ -37,3 +37,4 @@ component_management:
 # https://docs.codecov.com/docs/ignoring-paths
 ignore:
   - packages/aws-cdk/lib/cli.ts # we integ test this file
+  - ^(?!.*packages\/(aws-cdk|aws-cdk-lib\/core)\/).+$ # ignore anything that isn't in the cli or core