[AWS::CodeBuild::Project] - [Coverage] - Set Environment host-kernel property

### Name of the resource

AWS::CodeBuild::Project

### Resource name

AWS::CodeBuild::Project Environment

### Description

Support setting the new host-kernel property on the AWS::CodeBuild::Project Environment

Valid values:
- LINUX_KERNEL_4 (Amazon Linux 2),
- LINUX_KERNEL_6 (Amazon Linux 2023),
- LINUX_KERNEL_LATEST

### Other Details

Release announcement: https://aws.amazon.com/about-aws/whats-new/2026/07/aws-codebuild-amazon-linux-2023/
CLI Docs: https://docs.aws.amazon.com/cli/latest/reference/codebuild/create-project.html

Start with the AWS::CodeBuild::Project Environment resource and read the linked CodeBuild CLI documentation and release announcement for the host-kernel property. Locate the repository's implementation and validation entry points for this resource; done means the property accepts LINUX_KERNEL_4, LINUX_KERNEL_6, and LINUX_KERNEL_LATEST.

Written by the indexing model from the issue text.