fix(trigger): use oldest param for conversations.history consistency

Author: waleedlatif1

apps/sim/lib/webhooks/utils.server.ts

@@ -693,7 +693,7 @@ async function fetchSlackMessageText(
   try {
     const params = new URLSearchParams({
       channel,
-      latest: messageTs,
+      oldest: messageTs,
       inclusive: 'true',
       limit: '1',
     })