TargetExtType values are replaced with calls to `llvm.spv.track.constant`, with a `poison` value, but `llvm.spv.assign.type` was called with their original value. This PR updates the `assign.type` call to be consistent with the `track.constant` call. Fixes #134417. --------- Co-authored-by: Steven Perron <stevenperron@google.com>