automation: capture additional exception when formatting

I started encountering this for some reason.

Differential Revision: https://phab.mercurial-scm.org/D7078

contrib/automation/hgautomation/winrm.py

@@ -55,7 +55,7 b' def format_object(o):'
 
     try:
         o = str(o)
-    except TypeError:
+    except (AttributeError, TypeError):
         o = pprint.pformat(o.extended_properties)
 
     return o