Migrate to cargo_embargo. am: b6eaca7d40 am: 13678cd664

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/serde_spanned/+/2828071

Change-Id: I7d5a9b0837965c0c5f83545bcfce0b2a9288dfcb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>