Minor test fix in PyPy.

tests/run/strmethods.pyx

@@ -116,9 +116,9 @@ def mod_format(str s, values):
     True
     >>> mod_format(format2, ('XYZ', 'ABC')) == 'abcXYZdefABCghi'  or  mod_format(format2, ('XYZ', 'ABC'))
     True
-    >>> mod_format(None, 'sa')
+    >>> mod_format(None, 'sa')  # doctest: +ELLIPSIS
     Traceback (most recent call last):
-    TypeError: unsupported operand type(s) for %: 'NoneType' and 'str'
+    TypeError: ...NoneType...
     >>> class RMod(object):
     ...     def __rmod__(self, other):
     ...         return 123