Address Serhiy's review

Co-Authored-By: Serhiy Storchaka <3659035+serhiy-storchaka@users.noreply.github.com>

Author: Fidget-Spinner

Lib/test/test_xml_etree.py

@@ -1749,6 +1749,8 @@ def __next__(self):
     def test_unknown_event(self):
         with self.assertRaises(ValueError):
             ET.XMLPullParser(events=('start', 'end', 'bogus'))
+        with self.assertRaisesRegex(ValueError, "unknown event 'bogus'"):
+            ET.XMLPullParser(events=(x.decode() for x in (b'start', b'end', b'bogus')))
 
     @unittest.skipIf(pyexpat.version_info < (2, 6, 0),
                      f'Expat {pyexpat.version_info} does not '