fmq_unit_tests: Detect leaked FDs more efficiently am: 8676f1dbd6 am: 3d765532b9

Original change: https://android-review.googlesource.com/c/platform/system/libfmq/+/3108669

Change-Id: I7a4996a366c471afb68f0a4012dd6c9d0260acd4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>