Update variables.tf : Validation Check Fix

[vaibhavkumar779]

Updated variable value for permission of storage

Description

The validation check for per permissions for storage in legacy policies for key vault have a small typo failing the terraform code. So corrected the value.

Type of Change

• Non-module change (e.g. CI/CD, documentation, etc.)
• Azure Verified Module updates:
  • Bugfix containing backwards compatible bug fixes
    • Someone has opened a bug report issue, and I have included "Closes #{bug_report_issue_number}" in the PR description.
    • The bug was found by the module author, and no one has opened an issue to report it yet.
  • Feature update backwards compatible feature updates.
  • Breaking changes.
  • Update to documentation

Checklist

• I'm sure there are no other open Pull Requests for the same update/change
• My corresponding pipelines / checks run clean and green without any errors or warnings
• I did run all pre-commit checks

[matt-FFFFFF]

Thank you for your PR! LGTM