Update TEST_MAPPING am: fa4b6b3a8a

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt-derive/+/2108609

Change-Id: I625c249415b5bad642d2b94ea6f3a9f374f7f38a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>