Curl#curl_headers: Work with 8 exit_status

I recently noticed that ~23 `livecheck` blocks using the `HeaderMatch`
strategy were failing. Looking into it, these fail when using a `HEAD`
request and retry with `GET` but the resulting response with the
headers we want is simply discarded because the `exit_status` from
curl is 8 ("weird server reply").

This resolves the issue by adding a special case for this exit status,
so `#curl_headers` will return the headers in this scenario.

Library/Homebrew/utils/curl.rb

@@ -223,7 +223,7 @@ def curl_headers(*args, wanted_headers: [], **options)
         )
 
         # 22 means a non-successful HTTP status code, not a `curl` error, so we still got some headers.
-        if result.success? || result.exit_status == 22
+        if result.success? || result.exit_status == 8 || result.exit_status == 22
           parsed_output = parse_curl_output(result.stdout)
 
           if request_args.empty?
@@ -235,7 +235,7 @@ def curl_headers(*args, wanted_headers: [], **options)
             next if (400..499).cover?(parsed_output.fetch(:responses).last&.fetch(:status_code).to_i)
           end
 
-          return parsed_output if result.success?
+          return parsed_output if result.success? || result.exit_status == 8
         end
 
         result.assert_success!