chore: fix codeowner team name (#856)

This was using an incorrect name. The correct name is
@aws/aws-cdk-core-team.

## Was

<img width="720" height="517" alt="image"
src="https://github.com/user-attachments/assets/8b329077-8d96-40e6-bcf2-2c14526b1b35"
/>

## Now

<img width="458" height="339" alt="image"
src="https://github.com/user-attachments/assets/ab854646-4086-4e53-8e68-64520dcf12d0"
/>

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

Author: mrgrain

packages/cdk-assets/.github/CODEOWNERS

@@ -1,4 +1,4 @@
-/.github/ @cdk-core-team
-/bin/ @cdk-core-team
-/lib/ @cdk-core-team
-/test/ @cdk-core-team
+/.github/ @aws/aws-cdk-core-team
+/bin/ @aws/aws-cdk-core-team
+/lib/ @aws/aws-cdk-core-team
+/test/ @aws/aws-cdk-core-team