Update test_wsgiref.py

Author: benediktjohannes

Lib/test/test_wsgiref.py

@@ -853,8 +853,8 @@ def testRaisesControlCharacters(self):
         for c0 in control_characters_c0():
             with self.subTest(c0):
                 base = BaseHandler()
-                headers = Headers()
-                headers['key'] = f"val"
+                test = [('x','y')]
+                headers = Headers(test[:])
                 headers.add_header("key", "val")
                 # HTAB (\x09) is allowed in values, but not in names.
                 if c0 == "\t":