tests: Use subTest in test_bugdown_fixtures.

zerver/tests/test_bugdown.py

@@ -302,6 +302,7 @@ class BugdownTest(ZulipTestCase):
             else:
                 converted = bugdown_convert(test['input'])
 
+            with self.subTest(markdown_test_case=name):
                 print("Running Bugdown test %s" % (name,))
                 self.assertEqual(converted, test['expected_output'])