update Iterator Sequencing tests to reflect May 2025 plenary updates

[michaelficarra]

These tests should match the spec changes in tc39/proposal-iterator-sequencing#26.

[iamstolis]

Shouldn't built-ins/Iterator/concat/next-method-returns-throwing-value.js be updated as well? iterator.next() did not throw before because iteratorResult was reused (i.e. its value was not read). Now, IteratorStepValue() always reads the value of the inner iterator (which throws in this case). So, iterator.next() should throw now, right?

In other words, I think that 71794b1 should be reverted now.