RequestServer: Don't update Content-Length during cache revalidation

We were treating Content-Type as exempt from header updates during cache
revalidation and incorrectly allowing Content-Length to get overwritten
when handling an HTTP 304 response.

This caused cached entries to end up with a mismatched Content-Length
that described the validating response instead of the stored body.

Author: awesomekling

Services/RequestServer/Cache/Utilities.cpp

@@ -278,7 +278,7 @@ void update_header_fields(HTTP::HeaderMap& stored_headers, HTTP::HeaderMap const
         // * Header fields that are automatically processed and removed by the recipient, as described below, and
 
         // * The Content-Length header field.
-        if (name.equals_ignoring_ascii_case("Content-Type"sv))
+        if (name.equals_ignoring_ascii_case("Content-Length"sv))
             return true;
 
         return false;