Add "http.rb" to bot user agent substrings

This will cover Mastodon as well as some other Ruby-based scrapers.

tildes/tildes/request_methods.py

@@ -24,6 +24,7 @@ def is_bot(request: Request) -> bool:
     bot_user_agent_substrings = (
         "bingbot",
         "Googlebot",
+        "http.rb",
         "qotnews scraper",
         "Prometheus",
         "Python-urllib",