mtr: plugin.multiauth aix fix

The error loading the client module is different

mysql-test/suite/plugins/r/multiauth,aix.rdiff

@@ -0,0 +1,14 @@
+diff --git a/mysql-test/suite/plugins/r/multiauth.result b/mysql-test/suite/plugins/r/multiauth.result
+index aed46ac8964..24bb0a24f03 100644
+--- a/mysql-test/suite/plugins/r/multiauth.result
++++ b/mysql-test/suite/plugins/r/multiauth.result
+@@ -181,7 +181,8 @@ show create user mysqltest1;
+ CREATE USER for mysqltest1@%
+ CREATE USER `mysqltest1`@`%` IDENTIFIED VIA ed25519 USING 'F4aF8bw7130VaRbdLCl4f/P/wkjDmgJXwWvpJ5gmsZc'
+ # no plugin = failure
+-mysqltest: Could not open connection 'default': 1045 Plugin client_ed25519 could not be loaded: <PLUGINDIR>/no/client_ed25519.so: cannot open shared object file: No such file or directory
++mysqltest: Could not open connection 'default': 1045 Plugin client_ed25519 could not be loaded: Could not load module <PLUGINDIR>/no/client_ed25519.so.
++System error: No such file or directory
+ alter user mysqltest1 identified via ed25519 as password("good") OR mysql_native_password as password("works");
+ show create user mysqltest1;
+ CREATE USER for mysqltest1@%

mysql-test/suite/plugins/t/multiauth.test

@@ -1,4 +1,5 @@
 --source include/not_ubsan.inc
+--source include/platform.inc
 #
 # MDEV-11340 Allow multiple alternative authentication methods for the same user
 #