Migrate to cargo_embargo. am: 93b21ad4eb am: 2ad85522c7

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/async-task/+/2796114

Change-Id: Ife3ef8923065f3b327518c8154edffbe491a4202
Signed-off-by: Automerger Merge Worker <[email protected]>