feat(codebuild): add STANDARD_8_0, AMAZON_LINUX_2023_6 and AMAZON_LINUX_2023_STANDARD_4_0 images

[rgoltz]

Issue # (if applicable)

Closes #37586.

Reason for this change

AWS CodeBuild released new images on 2025-03-25 (release 26.03.25). CDK had no constants for these new images yet.

Description of changes

Added three new build image constants:

Constant	Image	Base OS
LinuxBuildImage.STANDARD_8_0	aws/codebuild/standard:8.0	Ubuntu 24.04
LinuxBuildImage.AMAZON_LINUX_2023_6	aws/codebuild/amazonlinux-x86_64-standard:6.0	Amazon Linux 2023
LinuxArmBuildImage.AMAZON_LINUX_2023_STANDARD_4_0	aws/codebuild/amazonlinux-aarch64-standard:4.0	Amazon Linux 2023 (ARM)

Updated README.md to include STANDARD_7_0, STANDARD_8_0 and AMAZON_LINUX_2023_6 in the example list of predefined images.

Describe any new or updated permissions being added

None.

Description of how you validated changes

Added unit tests for all three new constants in project.test.ts following the existing test.each pattern.

Updated integration tests for all three images (integ.project-standard-image.ts, integ.project-amazonlinux-image.lit.ts, integ.project-linux-arm.ts). All integration tests were deployed successfully and snapshots are included.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
This security report is NOT a review blocker. Please try merge from main to avoid findings unrelated to the PR.

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	Tests	Passed ✅	Skipped	Failed
Security Guardian Results	264 ran	264 passed

Test	Result
No test annotations available

• View Security Guardian Results

[github-actions]

⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
This security report is NOT a review blocker. Please try merge from main to avoid findings unrelated to the PR.

---

	Tests	Passed ✅	Skipped	Failed
Security Guardian Results with resolved templates	264 ran	264 passed

Test	Result
No test annotations available

• View Security Guardian Results with resolved templates