Skip a couple of libcore tests for gcstress config am: 114ac9ae57 am: ce3f131b73

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

Change-Id: Ic8fda3c168d8e963d6f3e802e364921d6e050aac
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>