main.processlist_notembedded fails in buildbot with Timeout in wait_until_count_sessions

main.processlist_notembedded             w1 [ fail ]

        Test ended at 2020-05-08 17:33:56

CURRENT_TEST: main.processlist_notembedded

mysqltest: In included file "/usr/share/mysql-test/include/wait_until_count_sessions.inc": 

included from /usr/share/mysql-test/t/processlist_notembedded.test at line 37:

At line 125: Timeout in wait_until_count_sessions.inc

The result from queries just before the failure was:

#

# MDEV-20466: SHOW PROCESSLIST truncates query text on \0 bytes

#

connect  con1,localhost,root,,;

connection con1;

SET DEBUG_SYNC= 'before_join_optimize SIGNAL in_sync WAIT_FOR go';

connection default;

SET DEBUG_SYNC= 'now WAIT_FOR in_sync';

FOUND 1 /sleep/ in MDEV-20466.text

SET DEBUG_SYNC= 'now SIGNAL go';

disconnect con1;

SET DEBUG_SYNC = 'RESET';

# Timeout in wait_until_count_sessions.inc

# Number of sessions   expected: <= 1   found: 2

SHOW PROCESSLIST;

Id	User	Host	db	Command	Time	State	Info	Progress

11071	root	localhost	test	Query	0	init	SHOW PROCESSLIST	0.000

11072	root	localhost	test	Query	10	debug sync point: before_join_optimize	SELECT user FROM mysql.user WHERE user ='some