Unit Tests: The `assertEqualSets()` helper was returning true for some sets that were not equal. `assertEqualSets()` now behaves correctly, and the new `assertEqualSetsWithIndex()` helper also checks that the array indexes are the same.

Fixes #30522.


git-svn-id: https://develop.svn.wordpress.org/trunk@30687 602fd350-edb4-49c9-b593-d223f7449a82