`#curl_headers` was recently introduced into `Strategy#page_headers`
but only the call was modified and the method wasn't updated to
correctly work with the new return value, so all `HeaderMatch` checks
immediately started failing with an error.
This commit includes changes that return `#page_headers` to a working
state. I've removed the `result.assert_success!` call because it
prevents a few checks from being retried with `GET` (`firefox-cn`,
`krisp`, `prepros`).
16f3a05e45