Update to syn-2 am: 4497fb4f59 am: a2ad5a30b1 am: 63b69f1f39 am: 0dc2c93a30

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

Change-Id: I78da38eb816f6e8d506b3c2c7dfedd0bae38e586
Signed-off-by: Automerger Merge Worker <[email protected]>