tests: Use a HttpRequest object in assert_login_failure.

Our convention is to always have authenticate() called with a request
object. We need to be consistent with that in tests too, to avoid test
failures resulting from breaking that assumption.
We modify assert_login_failure to call client.login() in the same way as
the other similar helpers - with a properly initialized HttpRequest
instance.

zerver/lib/test_classes.py

@@ -574,8 +574,11 @@ Output:
 
     def assert_login_failure(self, email: str, password: str) -> None:
         realm = get_realm("zulip")
+        request = HttpRequest()
+        request.session = self.client.session
         self.assertFalse(
             self.client.login(
+                request=request,
                 username=email,
                 password=password,
                 realm=realm,