Upgrade rust/crates/grpcio-compiler to 0.8.0 am: 70cf8c0afb

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/grpcio-compiler/+/1661951

Change-Id: I6c221cfb8b7d7cd8bb2759be86b9a1b1581a8392