Make GetItemSource(*, slice) hashable (#99379)
All Sources must be hashable, since we are using set equality to check for
duplicate sources in AOTAutograd. We should have a more systematic way
of asserting this. For this PR just fix the local issue.
Fixes #99145
Pull Request resolved: https://github.com/pytorch/pytorch/pull/99379
Approved by: https://github.com/ezyang
