test_faulthandler: fix typo

Author: vstinner

Lib/test/test_faulthandler.py

@@ -220,7 +220,7 @@ def test_disable(self):
             """
         not_expected = 'Fatal Python error'
         stderr, exitcode = self.get_output(code)
-        stder = '\n'.join(stderr)
+        stderr = '\n'.join(stderr)
         self.assertTrue(not_expected not in stderr,
                      "%r is present in %r" % (not_expected, stderr))
         self.assertNotEqual(exitcode, 0)