bug fix volume group show command.

There is no "show" function in the "group" class of python-cinderclient. Instead, there is a "get" function, so I fixed it.
0125495f92/cinderclient/v3/groups.py (L134)

Closes-Bug: #2111539
Change-Id: If61d8cf115c9ff04d172d7344565e693774e7a21

openstackclient/volume/v3/volume_group.py

@@ -552,7 +552,7 @@ class ShowVolumeGroup(command.ShowOne):
             parsed_args.group,
         )
 
-        group = volume_client.groups.show(group.id, **kwargs)
+        group = volume_client.groups.get(group.id, **kwargs)
 
         if parsed_args.show_replication_targets:
             replication_targets = (