MDEV-33242 Make Spider init queries compatible with non-default old_mode

Add UTF8_IS_UTF8MB3 to the (session) old_mode in connections made with
sql service to run init queries

The connection is new and the global variable value takes effect
rather than the session value from the caller of spider_db_init

storage/spider/mysql-test/spider/bugfix/r/mdev_33242.result

+set @old_old_mode=@@global.old_mode;
+set global old_mode=4;
+INSTALL SONAME 'ha_spider.so';
+set global old_mode=@old_old_mode;

storage/spider/mysql-test/spider/bugfix/t/mdev_33242.test

+set @old_old_mode=@@global.old_mode;
+set global old_mode=4;
+INSTALL SONAME 'ha_spider.so';
+set global old_mode=@old_old_mode;
+--disable_query_log
+--source ../../include/clean_up_spider.inc

storage/spider/spd_init_query.h

@@ -23,6 +23,9 @@ static LEX_STRING spider_init_queries[] = {
   {C_STRING_WITH_LEN(
     "SET @@SQL_MODE = REPLACE(@@SQL_MODE, 'ORACLE', '');"
   )},
+  {C_STRING_WITH_LEN(
+    "SET @@OLD_MODE = CONCAT(@@OLD_MODE, ',UTF8_IS_UTF8MB3');"
+  )},
   {C_STRING_WITH_LEN(
     "create table if not exists mysql.spider_xa("
     "  format_id int not null default 0,"