fix error reporting in xml test runner

Cython/Tests/xmlrunner.py

@@ -213,7 +213,7 @@ class _XMLTestResult(_TextTestResult):
         for tests in (self.successes, self.failures, self.errors):
             for test_info in tests:
                 if not isinstance(test_info, _TestInfo):
-                    print("Unexpected test result type: %s" % test_info)
+                    print("Unexpected test result type: %r" % (test_info,))
                     continue
                 testcase = type(test_info.test_method)