unit.conc_cursor test doesn't clean up

$ perl ./mtr unit.conc_cursor

<...>

==============================================================================

TEST                                      RESULT   TIME (ms) or COMMENT

--------------------------------------------------------------------------

worker[1] Using MTR_BUILD_THREAD 300, with reserved ports 16000..16019

unit.conc_cursor                         [ pass ]       

MTR's internal check of the test case 'unit.conc_cursor' failed.

This means that the test case does not preserve the state that existed

before the test case was executed.  Most likely the test case did not

do a proper clean-up. It could also be caused by the previous test run

by this thread, if the server wasn't restarted.

This is the diff of the states of the servers before and after the

test case was executed:

mysqltest: Logging to '/mnt-hd8t/src/10.6-bug/mysql-test/var/tmp/check-mysqld_1.log'.

mysqltest: Results saved in '/mnt-hd8t/src/10.6-bug/mysql-test/var/tmp/check-mysqld_1.result'.

mysqltest: Connecting to server localhost:16000 (socket /mnt-hd8t/src/10.6-bug/mysql-test/var/tmp/mysqld.1.sock) as 'root', connection 'default', attempt 0 ...

mysqltest: ... Connected.

mysqltest: Start processing test commands from './include/check-testcase.test' ...

mysqltest: ... Done processing test commands.

--- /mnt-hd8t/src/10.6-bug/mysql-test/var/tmp/check-mysqld_1.result	2021-07-19 18:42:06.986857805 +0300

+++ /mnt-hd8t/src/10.6-bug/mysql-test/var/tmp/check-mysqld_1.reject	2021-07-19 18:42:07.486861991 +0300

@@ -562,6 +562,7 @@

 def	sys	utf8mb3	utf8mb3_general_ci	NULL	

 def	test	latin1	latin1_swedish_ci	NULL	

 tables_in_test

+t10

 tables_in_mysql

 mysql.columns_priv

 mysql.column_stats

mysqltest: Result length mismatch

not ok