macos/grpc_basictests_c_cpp tests failing consistently after #23361 merged #23433
Description
Looks like it starts failing after #23361.
Sample: https://source.cloud.google.com/results/invocations/7f81a721-8584-4d46-b5d7-b09830bcee48/targets
D0709 10:38:17.922034000 140735797937024 test_config.cc:386] test slowdown factor: sanitizer=1, fixture=1, poller=1, total=1
E0709 10:38:17.923237000 140735797937024 sync_posix.cc:67] assertion failed: pthread_mutex_lock(mu) == 0
*******************************
Caught signal SIGABRT
no backtrace
Command terminated abnormally.
real 0.00
user 0.00
sys 0.00