Update TEST_MAPPING am: 39ff2874fc

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/rand_chacha/+/2399064

Change-Id: I00c7c8862433dc510c2fc5ea45e7d706e82412df
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>