Update test_wsgiref.py

Author: benediktjohannes

Lib/test/test_wsgiref.py

@@ -854,7 +854,6 @@ def testRaisesControlCharacters(self):
             with self.subTest(c0):
                 base = BaseHandler()
                 headers = Headers()
-                headers["key"] = f"val{c0}"
                 headers.add_header("key", "val")
                 # HTAB (\x09) is allowed in values, but not in names.
                 if c0 == "\t":