Fix bug preventing optimization from firing (#65573)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65573
When we remove mutation on
```
x = [0, 1, 3, 4]
x[-2] = 4
```
we have a safety check that the new index will be in bounds of the old index. in practice, this should always be the case otherwise you would have a runtime error. Within that check (not within the actual adjustment) we were using the wrong length of inputs preventing the optimization from firing.
Test Plan: Imported from OSS
Reviewed By: navahgar
Differential Revision: D31797469
Pulled By: eellison
fbshipit-source-id: 02a1686b9f6016eb5aeb87ed342c043c203dcd0e
