main.innodb_ext_key test case explain estimates 6 rows sometimes

CURRENT_TEST: main.innodb_ext_key

--- /home/buildbot/amd64-debian-11-msan/build/mysql-test/main/innodb_ext_key.result	2023-09-19 15:43:25.000000000 +0000

+++ /home/buildbot/amd64-debian-11-msan/build/mysql-test/main/innodb_ext_key.reject	2023-09-19 16:04:24.374253623 +0000

@@ -314,7 +314,7 @@

 select * from t0, part ignore index (primary)

 where p_partkey=t0.a and p_size=1;

 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

-1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	5	Using where

+1	SIMPLE	t0	ALL	NULL	NULL	NULL	NULL	6	Using where

 1	SIMPLE	part	eq_ref	i_p_size	i_p_size	9	const,dbt3_s001.t0.a	1	

 select * from t0,  part ignore index (primary)

 where p_partkey=t0.a and p_size=1;