Fix `assert_redirected_to` does not show user-supplied message.

Issue: when `assert_redirected_to` fails due to the response redirect not
matching the expected redirect the user-supplied message (second parameter)
is not shown. This message is only shown if the response is not a redirect.
Merge pull request #10800 from 907th/fix-custom-message-for-assert_redirected_to

Fix #10842. `assert_redirected_to` does not show user-supplied message.