MDEV-22894: Mariabackup should not read [mariadb-client] option group

from configuration files

extra/mariabackup/xtrabackup.cc

@@ -1626,7 +1626,7 @@ static int prepare_export()
 }
 
 static const char *xb_client_default_groups[]= {
-    "client", "client-server", "client-mariadb", "mariadb-client", 0, 0, 0};
+    "client", "client-server", "client-mariadb", 0, 0, 0};
 
 static const char *backup_default_groups[]= {
     "xtrabackup", "mariabackup", "mariadb-backup", 0, 0, 0};

mysql-test/suite/mariabackup/options_check.result

@@ -4,3 +4,4 @@
 # Check for unknown options in "mariadb-backup" group
 # Check for options overwriting
 # Check if uknown options that follow --mysqld-args are ingored
+# Check if [mariadb-client] group is not loaded (MDEV-22894)

mysql-test/suite/mariabackup/options_check.test

@@ -51,3 +51,14 @@ exec $XTRABACKUP --defaults-file=$custom_cnf --backup --target-dir=$targetdir;
 --echo # Check if uknown options that follow --mysqld-args are ingored
 exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf --backup --target-dir=$targetdir --mysqld-args --unknown-option;
 --rmdir $targetdir
+
+--echo # Check if [mariadb-client] group is not loaded (MDEV-22894)
+--copy_file $MYSQLTEST_VARDIR/my.cnf $custom_cnf
+--append_file $custom_cnf
+[mariadb-client]
+user=bla
+password=bla
+EOF
+exec $XTRABACKUP --defaults-file=$custom_cnf --backup --target-dir=$targetdir;
+--remove_file $custom_cnf
+--rmdir $targetdir