Add test for ConcurrentSkipListSet#headSet(E, boolean) am: 07d1ff87c6

Original change: https://googleplex-android-review.googlesource.com/c/platform/libcore/+/18234481

Change-Id: I895a83400ae0c88f541d6e876dba39c3751b9ba6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>