fix: make nil report as no error & add test for duplicate version.

[matt-FFFFFF]

This PR replaces #225 to enable CI/CD checks with required secrets.

Original PR by @kewalaka

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This pull request improves error handling and test coverage for the addPolicyAndRoleAssets method in alzlib.go, ensuring that duplicate policy and policy set definition versions are handled correctly. The changes refactor how errors are accumulated and reported, and add targeted unit tests for duplicate version scenarios.

Error handling improvements:

• Refactored error accumulation in addPolicyAndRoleAssets to use multierror.Append for both policy definitions and policy set definitions, ensuring errors are wrapped with descriptive context and reported correctly.

Testing enhancements:

• Added the TestAddPolicyAndRoleAssetsAllowsDuplicateVersions unit test to verify that adding duplicate versions of policy and policy set definitions works as expected, both when overwriting is allowed and disallowed.
• Introduced helper functions testPolicyDefinition and testPolicySetDefinition to simplify test setup for policy assets.

fixes: Azure/terraform-provider-alz#188
& Azure/terraform-provider-alz#189

[codecov-commenter]

Codecov Report

❌ Patch coverage is 20.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.98%. Comparing base (95f707a) to head (bba7879).

Files with missing lines	Patch %	Lines
alzlib.go	20.00%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #226      +/-   ##
==========================================
+ Coverage   49.37%   49.98%   +0.61%     
==========================================
  Files          49       49              
  Lines        4794     3929     -865     
==========================================
- Hits         2367     1964     -403     
+ Misses       2164     1702     -462     
  Partials      263      263              

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[jaredfholgate]

LGTM