fix stand by bug

Author: nasc17

src/azure-cli/azure/cli/command_modules/rdbms/flexible_server_custom_postgres.py

@@ -464,6 +464,7 @@ def flexible_server_update_custom_func(cmd, client, instance,
                             backup=instance.backup,
                             administrator_login=administrator_login,
                             administrator_login_password=administrator_login_password,
+                            availability_zone=instance.availability_zone,
                             maintenance_window=instance.maintenance_window,
                             network=instance.network,
                             identity=identity,

src/azure-cli/azure/cli/command_modules/rdbms/validators.py

@@ -541,7 +541,7 @@ def _pg_high_availability_validator(high_availability, zonal_resiliency, allow_s
                                      "To proceed, please set --allow-same-zone.")
 
     if standby_availability_zone:
-        if not high_availability_zone_redundant or not zonal_resiliency_enabled:
+        if not high_availability_zone_redundant and not zonal_resiliency_enabled:
             raise ArgumentUsageError("You need to enable high availability by setting --zonal-resiliency to Enabled "
                                      "to set standby availability zone.")
         if zone == standby_availability_zone: