attribute: add TestNotEquivalence and equality operator tests

[pellared]

Related to #7970

Add missing unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.7%. Comparing base (a866564) to head (f141b10).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #7979   +/-   ##
=====================================
  Coverage   81.7%   81.7%           
=====================================
  Files        304     304           
  Lines      23342   23342           
=====================================
+ Hits       19087   19089    +2     
+ Misses      3866    3864    -2     
  Partials     389     389           

see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[Copilot]

Pull request overview

Adds missing unit test coverage around attribute equivalence behavior, including direct == comparisons, in support of the ongoing work to support new attribute types (Issue #7970).

Changes:

• Extend TestEquivalence with direct equality-operator (==) checks for attribute.KeyValue.
• Add TestNotEquivalence to validate non-equivalent KeyValue pairs across Distinct, Set, and == comparisons.
• Remove a redundant assertion message in the existing equivalence test.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.