test_pep277: format function argument with ascii() on failure

"%a" instead of "%r"

Lib/test/test_pep277.py

@@ -98,7 +98,7 @@ class UnicodeFileTests(unittest.TestCase):
         if isinstance(exc_filename, bytes):
             filename = filename.encode(sys.getfilesystemencoding())
         if check_fn_in_exception:
-            self.assertEqual(exc_filename, filename, "Function '%s(%r) failed "
+            self.assertEqual(exc_filename, filename, "Function '%s(%a) failed "
                              "with bad filename in the exception: %r" %
                              (fn.__name__, filename, exc_filename))