Update Lib/test/test_wsgiref.py

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: benediktjohannes

Lib/test/test_wsgiref.py

@@ -860,7 +860,7 @@ def testRaisesControlCharacters(self):
             with self.subTest(c0):
                 base = BaseHandler()
                 headers = [('x','y')]
-                self.assertRaises(ValueError, base.start_response, f"{c0}", headers)
+                self.assertRaises(ValueError, base.start_response, c0, headers)
 
 
 class TestModule(unittest.TestCase):