Fix test_type_lookup_mro_reference test because it raises exception while type initialized

- in the old realisation this exception swallowed and this base not checked
  while finding in mro. so we don't change observed behavior with this
  change.

Author: sergey-miryanov

Lib/test/test_descr.py

@@ -5236,7 +5236,10 @@ def __hash__(self):
                 return hash('mykey')
 
             def __eq__(self, other):
-                X.__bases__ = (Base2,)
+                try:
+                    X.__bases__ = (Base2,)
+                except NameError:
+                    pass
 
         class Base(object):
             mykey = 'from Base'