Upgrade CodeBuild image to Amazon Linux 2023 standard 6.0

[agasthik]

Summary

Upgrades the CodeBuild environment image used by both the single-account and multi-account assessment stacks from the Amazon Linux 2 standard 4.0 image to the Amazon Linux 2023 standard 6.0 image.

The previous aws/codebuild/amazonlinux2-x86_64-standard:4.0 image is an older generation (AL2) on the path to deprecation. Moving to aws/codebuild/amazonlinux-x86_64-standard:6.0 (AL2023) keeps the build environment on a current, supported image with up-to-date default runtimes.

Changes

• deployment/aiml-security-single-account.yaml — CodeBuild Image updated to aws/codebuild/amazonlinux-x86_64-standard:6.0
• deployment/2-aiml-security-codebuild.yaml — same image update for the multi-account stack
• .gitignore — ignore .codex/, .pytest_cache/, and .ash/

Compatibility notes

• buildspec.yml pins python: 3.12 under runtime-versions, which the AL2023 standard 6.0 image supports — no buildspec change required.
• The AL2023 image ships newer default toolchain versions (Python, Node, etc.) than AL2 4.0.

Testing

• An assessment was run end-to-end on the new AL2023 6.0 image; the build provisioned correctly and the assessment Step Function completed successfully.