fix: safe navigate adapter_name for payload connection (#593)

In some cases, the payload connection may be nil, which we should handle
gracefully.

lib/honeybadger/notification_subscriber.rb

@@ -59,7 +59,7 @@ def format_payload(payload)
   class ActiveRecordSubscriber < NotificationSubscriber
     def format_payload(payload)
       {
-        query: Util::SQL.obfuscate(payload[:sql], payload[:connection].adapter_name),
+        query: Util::SQL.obfuscate(payload[:sql], payload[:connection]&.adapter_name),
         async: payload[:async]
       }
     end