Allow xtrabackup 9.6 to take backup of older server versions

if server version is 9.5 or below, allow xtrabackup to take backups of the server.

Author: satya-bodapati

storage/innobase/xtrabackup/src/backup_mysql.cc

@@ -421,7 +421,7 @@ bool check_server_version(unsigned long version_number,
   pxb24 = pxb24 || ((version_number > 100000 && version_number < 100300) &&
                     server_flavor == FLAVOR_MARIADB);
   // we will use xtrabckup 9.1 from server versions 9.1 to 9.6.
-  mysql9x = pxb_version == "9.1" &&
+  mysql9x = pxb_version == "9.6" &&
             (version_number >= 90100 && version_number < 90700);
 
   if (!mysql9x && pxb_version != server_version) {