🧪 Add missing tests for expectEnum

[akutuva21]

🎯 What: Added tests for the previously untested expectEnum utility in scripts/validate-metadata.js.
📊 Coverage: Covered happy path (valid enum values) as well as edge and error cases: invalid strings, numbers, booleans, objects, null, and undefined values.
✨ Result: Improved test coverage for metadata validation scripts to ensure reliable enum constraint enforcement.

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PR created automatically by Jules for task 14705957736384652318 started by @akutuva21

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