fix unchecked cast alias analysis (#32309)
Summary:
Unchecked cast just refines the type of a value, the value stays the same, so the output should alias the input.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32309
Differential Revision: D19439037
Pulled By: eellison
fbshipit-source-id: fe6902d0d9a5a9ef5e9c13e1dbd056576d8c327e
