Set max_microversion 2.56 for ServerPersonalityTestJSON

In compute microversion 2.57, the personality is removed from the server
create and rebuild APIs, also the maxPersonality and maxPersonalitySize
limits are excluded from the GET /limits API response, so this is to
set max_microversion 2.56 for ServerPersonalityTestJSON.

Change-Id: I3490fc329f9a5de8baa06357db581a6dacd791c7
diff --git a/tempest/api/compute/servers/test_server_personality.py b/tempest/api/compute/servers/test_server_personality.py
index ba2adbb..8a05e7a 100644
--- a/tempest/api/compute/servers/test_server_personality.py
+++ b/tempest/api/compute/servers/test_server_personality.py
@@ -29,6 +29,7 @@
 
 class ServerPersonalityTestJSON(base.BaseV2ComputeTest):
     """Test servers with injected files"""
+    max_microversion = '2.56'
 
     @classmethod
     def setup_credentials(cls):