server.security_groups is a list of dicts (#48798)

os_server was trying to access `[sg.name for sg in
server.security_groups]`, but the items in `server.security_groups`
are dictionaries, so that should be `sg['name']`.

lib/ansible/modules/cloud/openstack/os_server.py

@@ -625,7 +625,7 @@ def _check_security_groups(module, cloud, server):
         return changed, server
 
     module_security_groups = set(module.params['security_groups'])
-    server_security_groups = set(sg.name for sg in server.security_groups)
+    server_security_groups = set(sg['name'] for sg in server.security_groups)
 
     add_sgs = module_security_groups - server_security_groups
     remove_sgs = server_security_groups - module_security_groups