chore(cloud-assembly-schema): rename report file

[kaizencc]

Rename from policy-validation-report.json to validation-report.json to avoid conflicting with the existing report format written by aws-cdk-lib which uses a different schema shape.

Fixes #

Checklist

• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
  • Release notes for the new version:

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.16%. Comparing base (5218062) to head (ac5dc6b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1542      +/-   ##
==========================================
- Coverage   88.18%   88.16%   -0.02%     
==========================================
  Files          76       76              
  Lines       10839    10839              
  Branches     1493     1494       +1     
==========================================
- Hits         9558     9556       -2     
- Misses       1253     1255       +2     
  Partials       28       28              

Flag	Coverage Δ
suite.unit	88.16% <ø> (-0.02%)	⬇️

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