MDEV-21360 save/restore debud_dbug instead of total reset at the end of the test

mysql-test/extra/rpl_tests/rpl_corruption.inc

@@ -74,7 +74,6 @@ while ($i) {
 # Emulate corruption in binlog file when SHOW BINLOG EVENTS is executing
 --echo # 2. Corruption in master binlog and SHOW BINLOG EVENTS
 set @saved_dbug = @@global.debug_dbug;
-
 SET GLOBAL debug_dbug="+d,corrupt_read_log_event_char";
 --echo SHOW BINLOG EVENTS;
 --disable_query_log

mysql-test/extra/rpl_tests/rpl_parallel.inc

@@ -1651,6 +1651,7 @@ SELECT * FROM t2 WHERE a >= 40 ORDER BY a;
 --sync_with_master
 SELECT * FROM t2 WHERE a >= 40 ORDER BY a;
 --source include/stop_slave.inc
+SET GLOBAL debug_dbug=@old_dbug;
 SET DEBUG_SYNC= 'RESET';
 SET GLOBAL slave_parallel_threads=0;
 SET GLOBAL slave_parallel_threads=10;

mysql-test/suite/binlog_encryption/rpl_parallel.result

@@ -1227,6 +1227,7 @@ a
 45
 46
 include/stop_slave.inc
+SET GLOBAL debug_dbug=@old_dbug;
 SET DEBUG_SYNC= 'RESET';
 SET GLOBAL slave_parallel_threads=0;
 SET GLOBAL slave_parallel_threads=10;

mysql-test/suite/rpl/r/rpl_parallel.result

@@ -1226,6 +1226,7 @@ a
 45
 46
 include/stop_slave.inc
+SET GLOBAL debug_dbug=@old_dbug;
 SET DEBUG_SYNC= 'RESET';
 SET GLOBAL slave_parallel_threads=0;
 SET GLOBAL slave_parallel_threads=10;