fix: Terraform variable validation

[patrickmoore-nc]

Description

Fix some errors in a recent change to validate more Terraform input variables.

Testing

Hub non-live now plans ok:
https://dev.azure.com/nhse-dtos/dtos-hub/_build/results?buildId=19958&view=results

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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[saliceti]

I've seen another error:

   on ../../dtos-devops-templates/infrastructure/modules/firewall-policy/variables.tf line 5, in variable "policy_name":
│    5:     condition     = can(regex("^[a-zA-Z0-9_][a-zA-Z0-9-_]{0,78}[a-zA-Z0-9_]$", var.name))