Ladybird+LibWeb+WebContent: Port the did_request_cookie IPC to String

Author: https://github.com/trflynn89
Commit: 85b8971a80
Pull-request: https://github.com/SerenityOS/serenity/pull/22951

Userland/Utilities/headless-browser.cpp

@@ -168,7 +168,7 @@ private:
                 on_scroll_to_point(position);
         };
 
-        on_get_cookie = [this](auto const& url, auto source) -> ByteString {
+        on_get_cookie = [this](auto const& url, auto source) {
             return m_cookie_jar.get_cookie(url, source);
         };