unsuport back deployment test

Author: huixie90

libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.wait/lost_wakeup.pass.cpp

@@ -8,6 +8,10 @@
 
 // UNSUPPORTED: no-threads
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// TODO: This test (unreliably) fails when back-deploying to macOS 15. However,
+//       we've only managed to observe the failure on the Github-provided CI
+//       runners, which is suspicious.
+// UNSUPPORTED: stdlib=system && target={{.+}}-apple-macosx15{{.*}}
 
 // This is a stress test for std::atomic::wait for lost wake ups.