Fix: default has_vulnerability_alerts to false

[Copilot]

• Change has_vulnerability_alerts default from true to false in modules/repository_base/variables.tf
• Add has_vulnerability_alerts variable (default false) to public/private/internal repository modules
• Wire var.has_vulnerability_alerts through to repository_base in all three sub-modules
• Pass has_vulnerability_alerts through in modules/repository_set/repositories.tf
• Update READMEs for all affected modules
• Add has_vulnerability_alerts = optional(bool, false) to public_repositories type in modules/repository_set/variables.tf (CI fix)
• Add has_vulnerability_alerts = optional(bool, false) to internal_repositories type in modules/repository_set/variables.tf (CI fix)
• Create .github/workflows/copilot-setup-steps.yml to pre-install Terraform for local validation

[seanpoulter-foci]

@copilot, the workflow failure should not happen. Please improve your own tooling and instructions to prevent this from happening. Use https://github.com/foci-github-foundations/organizations/blob/main/.github/workflows/copilot-setup-steps.yml for inspiration to ensure the required tools are available.

[Copilot]

@copilot, the workflow failure should not happen. Please improve your own tooling and instructions to prevent this from happening. Use https://github.com/foci-github-foundations/organizations/blob/mai...

Fixed in feeb89f.

Two changes:

1. CI failure root cause: has_vulnerability_alerts was missing from the public_repositories and internal_repositories object type definitions in repository_set/variables.tf, so each.value.has_vulnerability_alerts failed with "Unsupported attribute". Added has_vulnerability_alerts = optional(bool, false) to both.

2. Tooling: Added .github/workflows/copilot-setup-steps.yml that pre-installs Terraform 1.9.8 (matching the version in the PR workflow), so future sessions can run terraform test locally to catch these errors before pushing.