MDEV-15522: Change galera suite MTR tests to use mariabackup instead of xtrabackup

Disable galera tests using xtrabackup.

Author: Jan Lindström

mysql-test/suite/galera/disabled.def

@@ -42,3 +42,10 @@ galera_as_slave_replication_budle : MDEV-15785 Test case galera_as_slave_replica
 galera_wan : MDEV-17259: Test failure on galera.galera_wan
 galera_pc_ignore_sb : MDEV-17357 Test failure on galera.galera_pc_ignore_sb
 galera_drop_database : test
+galera_autoinc_sst_xtrabackup : xtrabackup is deprecated
+galera_ist_xtrabackup-v2 : xtrabackup is deprecated
+galera_sst_xtrabackup-v2_data_dir : xtrabackup is deprecated
+galera_sst_xtrabackup-v2_encrypt_with_key : xtrabackup is deprecated
+galera_sst_xtrabackup-v2-options : xtrabackup is deprecated
+galera_ist_innodb_flush_logs : xtrabackup is deprecated
+galera_sst_xtrabackup-v2 : xtrabackup is deprecated