fix(release): correct module reference version updates and add safety tests

[nhs-oliverslater]

Description

• Fix release updater behavior for local module source version replacements under infrastructure/modules.
• Fix handling of version formats so both plain and v-prefixed versions are updated correctly.
• Fix pinning behavior so pin and unpin controls apply only to Terraform source files.
• Keep README updates automatic for terraform-docs generated content.
• Add and validate a smoke test for release updater behaviour across normal, pinned, and unpinned cases.

Context

Type of changes

• Refactoring (non-breaking change)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would change existing functionality)
• Bug fix (non-breaking change which fixes an issue)

Checklist

• I am familiar with the contributing guidelines
• I have followed the code style of the project
• I have added tests to cover my changes
• I have updated the documentation accordingly
• This PR is a result of pair or mob programming

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• I confirm that neither PII/PID nor sensitive data are included in this PR and the codebase changes.