Bump brace-expansion from 1.1.15 to 1.1.18 in /testing/aws-testing-cdk - #7081

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02, codecov/codecov-action@29386c70ef20e286228c72b668a06fd0e8399192. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/