MDEV-34617 galera.galera_ist_mariabackup_verify_ca fails on FreeBSD

Was failing because innodb-log-file-buffering is a Linux/Windows only
variable.

This was introduced in MDEV-33787 to enforce O_DIRECT on Linux.

mysql-test/suite/galera/t/galera_ist_mariabackup_verify_ca.cnf

@@ -10,11 +10,11 @@ ssl-ca=@ENV.MYSQL_TEST_DIR/std_data/cacert.pem
 
 [mysqld.1]
 wsrep_provider_options='base_port=@mysqld.1.#galera_port;pc.ignore_sb=true'
-innodb-log-file-buffering
+loose-innodb-log-file-buffering
 
 [mysqld.2]
 wsrep_provider_options='base_port=@mysqld.2.#galera_port;pc.ignore_sb=true'
-innodb-log-file-buffering
+loose-innodb-log-file-buffering
 
 [sst]
 ssl-mode=VERIFY_CA