Migrate to cargo_embargo. am: 5f3de4f5b9

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro-nested/+/2832460

Change-Id: I0ee5b74f7f064e75c4da5d196a1ab158d1eb4dff
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>