MDEV-22020: Fix spider/bugfix.return_found_rows_update

The test failed to specify default-character-set when
invoking the client. The compile-time default parameters of the
client could be overridden by configuration files in /etc/mysql.
Let us explicitly specify --default-character-set.

storage/spider/mysql-test/spider/bugfix/t/return_found_rows_update.test

@@ -54,7 +54,7 @@ TRUNCATE TABLE mysql.general_log;
 
 --disable_query_log
 echo EXE_MYSQL -v -v -u root -h localhost -P MASTER_1_MYPORT -S MASTER_1_MYSOCK -e "UPDATE tbl_a SET tm = '12:00:00' WHERE skey = 0" auto_test_local;
-exec $EXE_MYSQL -v -v -u root -h localhost -P $MASTER_1_MYPORT -S $MASTER_1_MYSOCK -e "UPDATE tbl_a SET tm = '12:00:00' WHERE skey = 0" auto_test_local;
+exec $EXE_MYSQL -v -v -u root -h localhost --default-character-set=latin1 -P $MASTER_1_MYPORT -S $MASTER_1_MYSOCK -e "UPDATE tbl_a SET tm = '12:00:00' WHERE skey = 0" auto_test_local;
 --enable_query_log
 
 --connection child2_1