Fix a sys_vars.all_vars failure caused by Bug #56680 instrumentation.

The variable innodb_change_buffering_debug is only present in debug builds.
Hide it from the test, so that the test passes in both debug and non-debug.

mysql-test/suite/sys_vars/r/all_vars.result

@@ -3,6 +3,7 @@ create table t2 (variable_name text);
 load data infile "MYSQLTEST_VARDIR/tmp/sys_vars.all_vars.txt" into table t1;
 insert into t2 select variable_name from information_schema.global_variables;
 insert into t2 select variable_name from information_schema.session_variables;
+delete from t2 where variable_name='innodb_change_buffering_debug';
 update t2 set variable_name= replace(variable_name, "PERFORMANCE_SCHEMA_", "PFS_");
 select variable_name as `There should be *no* long test name listed below:` from t2
 where length(variable_name) > 50;

mysql-test/suite/sys_vars/t/all_vars.test

@@ -61,6 +61,9 @@ eval load data infile "$MYSQLTEST_VARDIR/tmp/sys_vars.all_vars.txt" into table t
 insert into t2 select variable_name from information_schema.global_variables;
 insert into t2 select variable_name from information_schema.session_variables;
 
+# This is only present in debug builds.
+delete from t2 where variable_name='innodb_change_buffering_debug';
+
 # Performance schema variables are too long for files named
 # 'mysql-test/suite/sys_vars/t/' ...
 # ... 'performance_schema_events_waits_history_long_size_basic-master.opt'