[Sheriff] Mark test-debug/* as flaky on Mac.

test/cctest/cctest.status

Index: test/cctest/cctest.status
diff --git a/test/cctest/cctest.status b/test/cctest/cctest.status
index c6bc1e7a2e9cdb28bd515b306773a03ca72e4b15..e6729aff2bc838eb5338441ef0ebfcf647aa4597 100644
--- a/test/cctest/cctest.status
+++ b/test/cctest/cctest.status
@@ -84,6 +84,13 @@
 }],  # 'system == windows'
 
 ##############################################################################
+['system == macos', {
+
+  # BUG(3125).
+  'test-debug/*': [PASS, ['mode == debug', FLAKY]],
+}],  # 'system == macos'
+
+##############################################################################
 ['arch == arm', {
 
   # We cannot assume that we can throw OutOfMemory exceptions in all situations.