Add scoped Bicep lint validation

[WilliamBerryiii]

Description

Adds scoped Bicep lint validation so PR validation can focus lint work on changed folders instead of running broader validation unnecessarily.

Related Issue

• Closes Improve Bicep lint and validation CI performance #553

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• CI/CD pipeline change
• Security improvement
• Performance improvement
• Refactoring

Implementation Details

• Updates the Bicep lint workflow for scoped validation.
• Updates matrix folder-change detection and PR validation workflow wiring.
• Updates folder-change detection logic and test coverage in Detect-Folder-Changes.ps1.
• Updates Bicep lint invocation logic and test coverage in Invoke-BicepLint.ps1.

Changed files:

• .github/workflows/bicep-lint.yml
• .github/workflows/matrix-folder-check.yml
• .github/workflows/pr-validation.yml
• scripts/build/Detect-Folder-Changes.ps1
• scripts/build/Detect-Folder-Changes.Tests.ps1
• scripts/build/Invoke-BicepLint.ps1
• scripts/build/Invoke-BicepLint.Tests.ps1

Testing Performed

• Updated PowerShell test coverage for folder-change detection and Bicep lint invocation.
• CI validation is expected to run on this pull request.

Validation Steps

1. Open a PR with Bicep-related changes and confirm scoped Bicep lint runs for the affected folders.
2. Open a PR without Bicep-related changes and confirm unnecessary Bicep lint work is skipped.
3. Confirm PR validation still receives the expected changed-folder outputs.

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex logic where needed
• Documentation updated if required
• Tests added or updated
• No breaking changes introduced
• Security considerations reviewed

Security Review

• No secrets, tokens, credentials, or sensitive data are intentionally included.
• Changes are limited to CI workflow logic and build/test scripts.

Additional Notes

Branch diff summary: 7 files changed, 894 insertions, 103 deletions.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.41%. Comparing base (41b933a) to head (a78d8d0).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #559   +/-   ##
=======================================
  Coverage   32.41%   32.41%           
=======================================
  Files          40       40           
  Lines        5902     5902           
=======================================
  Hits         1913     1913           
  Misses       3989     3989           

Flag	Coverage Δ
rust	32.41% <ø> (ø)

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