fix(reddit): cache tweak for 403 forbidden (#3830)

lib/contents.php

@@ -71,6 +71,7 @@ function getContents(
                 // Ignore invalid 'Last-Modified' HTTP header value
             }
         }
+        // todo: to be nice nice citizen we should also check for Etag
     }
 
     $response = $httpClient->request($url, $config);

lib/http.php

@@ -2,6 +2,7 @@
 
 class HttpException extends \Exception
 {
+    // todo: should include the failing http response (if present)
 }
 
 final class CloudFlareException extends HttpException