test: adjust 6467 for `Int.reduceNeg` no longer stripping `no_index`

`Int.reduceNeg` now leaves `-(no_index 2)` untouched, so `simp only [Int.reduceNeg]` correctly reports no progress.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
1 file changed