The return hash from `#curl_http_content_headers_and_checksum`
contains a `:status`, which is the status code of the last response.
This string value comes from `#parse_curl_response`, where the key is
`:status_code` instead.
Aligning these keys technically allows us to pass either of these
hashes to the `#url_protected_by_*` methods, as both contain
`:status_code` and `:headers` in the expected format.
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