Skip a couple of libcore tests for gcstress config am: 114ac9ae57

Original change: https://android-review.googlesource.com/c/platform/art/+/2982035

Change-Id: Ic93d124790f17e9c56c36859d788d680c8ea78de
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>