Update to syn-2 am: 4497fb4f59 am: a2ad5a30b1 am: 63b69f1f39 am: 0dc2c93a30 am: 1240f58d0b am: 484f49320b

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/async-stream-impl/+/2522575

Change-Id: I5c2e527cac1efb0be6627dea7a8ed80d29efadce
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>