Actually update the max_packet size

This was tried with e596a3b but did still fail.

Author: vmcj

.github/jobs/baseinstall.sh

@@ -64,7 +64,7 @@ mysql_root "show databases"
 mysql_root "SELECT CURRENT_USER();"
 mysql_root "SELECT USER();"
 mysql_root "SELECT user,host FROM mysql.user"
-mysql_root "SET max_allowed_packet=1073741824"
+mysql_root "SET GLOBAL max_allowed_packet=1073741824"
 echo "unused:sqlserver:domjudge:domjudge:domjudge:3306" > /opt/domjudge/domserver/etc/dbpasswords.secret
 mysql_user "SELECT CURRENT_USER();"
 mysql_user "SELECT USER();"