feat: warn on invalid link

Instead of logging at the info level, warn when the link is unreachable.

Author: MightyCreak

src/Parser/UrlCache.php

@@ -114,7 +114,12 @@ private function updateUrl(string $url): void
         if ($urlHeader !== false) {
             $response = $urlHeader[0];
             $valid = $this->isValidResponse($response);
-            Mesamatrix::$logger->info("Try URL \"{$url}\": " . ($valid ? "valid" : "invalid") . " (\"{$response}\")");
+            if ($valid) {
+                Mesamatrix::$logger->info("URL \"{$url}\" is valid");
+            }
+            else {
+                Mesamatrix::$logger->warning("URL \"{$url}\" is invalid");
+            }
         }
 
         // Register URL's validity.